Full text of "The stone industries : dimension stone, crushed stone, geology, technology, distribution, utilization"

See other formats

university of

Connecticut

ibraries

BOOK 553.5.B68 c. 1
BOWLES # STONE INDUSTRIES

3 T1S3 D013b7flb 3

Digitized by the Internet Archive

in 2009 with funding from

Boston Library Consortium IVIember Libraries

http://www.archive.org/details/stoneindustriesdOObowl

THE STONE INDUSTRIES

.6Q

THE STONE INDUSTEIES "

Dimension Stone Crushed Stone

Geology Technology Distribution Utilization

OLIVER BOWLES

Supervising Engineer, Bxiilding Materials Section
United States Bureau of Mines

Second Edition

McGRAW-HILL BOOK COMPANY, Inc.

NEW YORK AND LONDON

1939

PRINTED IN THE UNITED STATES OF AMERICA

parts thereof, may not be reproduced

in any form without permission of

the publishers.

THE MAPLE PRESS COMPANY, YORK, PA.

PREFACE TO THE SECOND EDITION

Since the first edition of this volume appeared, the stone industries
have suffered the most severe depression in their history. Now they are
emerging toward a more normal rate of production, and there is definite
prospect of increasing activity in building which should promote further
gains. In this new edition most of the tables have been revised to show
the latest available figures, and corresponding changes have been made in
the text to embody the most recent data.

Centers of production have shown so Httle change during recent years
that only minor corrections were needed. The sections on technology
of quarrying and fabrication as covered in the first edition were based
largely on the author's personal observation and study of hundreds of
quarries and stone-finishing mills, and they reflect modern practice so
comprehensively that little revision was required. Although refinements
in equipment and methods are constantly in evidence, no fundamental
modifications have occurred since 1934; therefore, the portrayal of condi-
tions as set forth in the new edition approximates a true picture of the
stone industries as they exist today.

Oliver Bowles.
Washington, D. C,
January, 1939.

PREFACE TO THE FIRST EDITION

No book adequately covering the stone industries has been available
recently. Building stones were described many years ago by Dr. George
P. Merrill in his well-known volume, Stones for Building and Decoration,
the third edition of which appeared in 1910 and is now out of print.
The venerable doctor was planning a much-needed revision, but his
plans were cut short by his sudden death in 1929. Other books, such as
E. C. Eckel's Buildijig Stones and Clays and C. H. Richardson's volume
of the same title, are valuable for certain phases of the stone industries.
Various bulletins on granites, marbles, and slates by T. Nelson Dale
contain a wealth of detailed information, chiefly of geological import.
Bulletins of several State geological surveys describe the stone resources
and developments of their States quite thoroughly, but few have been
published during recent years. Certain textbooks for engineers and
architects contain brief and frequently quite inaccurate references to
stone as a material of construction. None of the publications mentioned
presumes to cover the many ramifications of the stone industries; the
purpose of this volume is to fill this gap in American technical literature.

The author began his studies of the stone industries in Minnesota in
1912; and during the years since 1914, as a quarry specialist of the
United States Bureau of Mines, he has visited and made intimate exami-
nations of hundreds of quarries and mills scattered throughout many
States. Results of successive detailed studies were embodied in a series
of reports, several of which are now out of print. The background of
first-hand knowledge thus gained was the chief incentive that urged him
toward the laborious task of compiling this book.

Acknowledgment is made to the officials of the United States Bureau
of Mines for permitting wide reference to its published information.
Grateful acknowledgment is rendered to many who have assisted in
preparing the material. In presenting a broad subject in a comprehen-
sive manner innumerable occasions for errors occur, and while mis-
statements may still remain, review by competent authorities and
repeated revisions have greatly minimized this liability. The author
desires to make special mention of noteworthy service by Harold Ladd
Smith of Proctor, Vt.; J. B. Newsom of Bloomington, Ind.; J. L. Mann
and R. M. Richter of Bedford, Ind.; Charles H. Behre of Evanston, 111.;
W. S. Hays of Philadelphia; Lawrence Childs and Jules Leroux of New
York, and Societe Anonyme de Merbes-Sprimont, Brussels, Belgium.
Several quarry operators have kindly reviewed sections of the book

vili PREFACE TO THE FIRST EDITION

relating to their industries. The chapters devoted to crushed and broken
stone involved so much detail regarding deposits and their geology that
the services of State geologists were enlisted for review and comment.
The author desires to express to them his keen appreciation of their
most helpful and hearty cooperation. To Paul M. Tyler, Paul Hatmaker,
and H. Herbert Hughes, associates of the author in the United States
Bureau of Mines, acknowledgment is due for many helpful suggestions.
Miss A. T. Coons of the Bureau, whose intimate knowledge of the stone-
producing industries is widely recognized, supplied valuable comment
and advice. To my wife, Eva H. Bowles, grateful acknowledgment is
made for assistance in proof reading, and to my sons, George and Edgar,
for corrections and revisions of certain sections.

Oliver Bowles.
Washington, D. C.
July, 1934

CONTENTS

Page

Preface to the Second Edition v

Preface to the First Edition vii

Introduction xiii

PART I

GENERAL FEATURES OF THE STONE INDUSTRIES

CHAPTER I
Extent and Subdivision 3

Extent of the Industry — Major Divisions of the Industry — Varieties of
Stone Used

CHAPTER II

Minerals and Rocks 5

Distinction between Rock and Stone — Relation of Rocks to Minerals —
Rock-forming Minerals — Classification of Rocks — General Distribution of
Rocks in the United States

CHAPTER III

Factors Governing Rock Utilization 8

Rock Qualities on Which Use Depends — Importance of Other Factors than
QuaUty — Available Markets — Diversification of Products — Transportation
Facilities — Production Costs

CHAPTER IV

Prospecting and Development II

Prospecting — Stripping— General Methods of Operation — Bibliography

PART II
DIMENSION STONE

CHAPTER V

General Features of Dimension-stone Industries 23

Definition of Dimension Stone — Principal Uses — Requisite QuaUties of
Dimension Stone — Adaptations of Raw Materials to Use — Complexities in
Marketing — Royalties

CHAPTER VI

Limestone 33

Definition: — Origin — Physical Properties — Varieties — Qualities on Which
Use Depends — Uses — Industry by States — Occurrences of Travertine —
Quarry Methods — MiUing Methods — Limestone Products — Cost of Quarry-
ing and Manufacture — Waste in Quarrying and Manufacture — Utilization
of Waste — Limestone Marketing — Bibliography

X CONTENTS

Page
CHAPTER VII

Sandstone 67

Varieties — Composition — Size and Shape of Grains — Cementation — Color —
Porosity — Uses — Production — Industry by States — Quarry Methods —
Quarry Processes — Yard Service — Sandstone Sawmills and Finishing Plants
— The Bluestone Industry — Waste in Sandstone Quarrying and Manufac-
ture— Bibliography

CHAPTER VIII

Granite 103

General Character — Mineral Composition — Chemical Composition — Physi-
cal Properties — Varieties — Related Rocks — Structural Features- — Uses —
Distribution of Deposits — Industry by States — Quarry Methods and Equip-
ment— Milling Methods and Equipment — Market Range — Imports,
Exports, and Tariffs — Prices — Bibliography

CHAPTER IX

Marble 168

History — Definition — Composition — Origin and Varieties — Physical Prop-
erties— Jointing or Unsoundness — Chief Impurities of Marble — Uses — Dis-
tribution of Deposits — Production — Industry by States — Quarry Methods
and Equipment — Transportation — Equipment and Operation in Mills and
Shops — Waste in Quarrying and Manufacture — Marketing Marble —
Imports and Exports — Tariff — Prices — Bibliography

CHAPTER X

Slate 229

Definition — Origin — Mineralogical Composition — Chemical Composition —
Physical Properties — Structural Features — Imperfections — Uses — History
of Industry — General Distribution — Production — Industry by States —
General Plan of Quarrying — Quarry Operations — Quarry Methods — Yard
Transportation — Manufacture of Roofing Slate — Storage of Roofing Slate —
The Art of Roofing with Slate — Manufacture of School Slates — Manufacture
of Mill Stock — Slate Floors, Walks, and Walls — Crushed and Pulverized
Slate Products — Waste in Quarrying and Manufacturing — Tests and
Specifications — Marketing — Imports and Exports — Tariff — Prices —
Bibliography

CHAPTER XI

SOAPSTONE 290

Composition and Properties — History — Uses — Origin and Occurrence —
Quarry Methods — Milling Processes — Marketing — Rocks Related to Soap-
stone — Bibliography

CHAPTER XII

Boulders as Building Materials 296

Origin and Nature of Boulders — Stone Fences — The Use of Boulders in
Buildings

CHAPTER XIII

Foreign Building and Ornamental Stones 301

Scope of Discussion — Imports of Stone — Foreign Limestones — Foreign

CONTENTS XI

Page
Sandstones — Foreign Granites — Foreign Marbles — Foreign Slates^ —
Bibliography

CHAPTER XIV

Miscellaneous Rocks and Minerals Used for Building and Ornamental

Purposes 342

Agalmatolite — Alabaster — Amazonite — Catlinite — Clay — Diatomite, Trip-
oli and Pumice — Fluorite — Jade — Labradorite — Lapis-lazuli — Malachite
and Azurite — Meerschaum — Mica Schist — Porphyry — Quartz — Snow and
Ice — Sodalite — Bibliography

CHAPTER XV

Deterioration, Preservation, and Cleaning of Stonework 348

Deterioration of Stone — Preservation of Stone — Cleaning Stone — Bibliog-
raphy

PART III
CRUSHED AND BROKEN STONE

CHAPTER XVI

General Features of the Crushed-stone Industries 371

History — Types and Values of Stone Used — Crushed Stone and Dimen-
sion Stone Contrasted — Uses of Crushed Stone — Competition — Markets —
Transportation — Prices — Royalties — Capital Required

CHAPTER XVII

Crushed and Broken Limestone 377

Types of Stone Included — Extent of Industry — Uses of Crushed and Broken
Limestone — Uses for Which Physical Properties Are Most Important — Uses
for Which Chemical Properties Are Most Important — Uses of Dolomite and
High-magnesian Limestone — Industry by States — Quarry Methods and
Equipment — Bibliography

CHAPTER XVIII

Crushed and Broken Stone Other Than Limestone 473

General Features — Uses — General Distribution and Value — Industries by
States — Quarry Methods and Equipment — Marketing — Bibliography

Index 493

INTRODUCTION

Stone, the foundation and superstructure of the everlasting hills,
is the most abundant of all material things. It is the earth itself on which
we live. Although widespread in occurrence to a point that breeds
contempt, stone is used so extensively that it touches the extremes of
human activity — from lowly shattered fragments trampled under foot
to flawless statuary marbles that provide material for the highest forms
of art. Between these two extremes stone and its products are essential
to multitudes of industries; they take part in the affairs of practically
every community and touch the life of nearly every person. To cover
in detail so broad a field would far exceed the scope of a single volume, but
an attempt is made to present a moderately comprehensive picture of the
properties and characteristics of stone, the methods of removing it from
its native beds and preparing it for use, its many applications in modern
industry, production centers at home and abroad, and the outstanding
economic features of each branch of this far-reaching industry.

Remarkable progress has been made in the quarrying and utilization
of stone. Its application to practical use was one of the oldest human
activities, extending far back before the earliest records, for the name
"stone age" is applied to that period of history of which knowledge is
conveyed to us only by crude tools and implements of stone fashioned
by the aborigines. Neolithic man, using a crooked reindeer antler as a
mining tool, dug flint balls from the chalk cliffs of England and shaped
them into spear heads or other implements. During later periods
American cliff-dwellers constructed crude homes with walls of stone.
The slow progress made through long ages from these primitive begin-
nings makes interesting chapters in ancient history but has little bearing
on the stone quarrying of today. Development of the industries in their
present scope has been comparatively recent. From caverns and shelter-
ing slabs of rock constituting the earliest human habitations to stately
mansions of cut and polished stone is a long journey, and every step of
progress has been marked by accelerated speed. Thus, although the
industries have existed for many centuries, the greatest advances in
manufacture and use have been crowded into the last fifty years. To
give a true picture of the status of these industries today is the purpose
of this book.

PART I
GENERAL FEATURES OF THE STONE INDUSTRIES

CHAPTER I
EXTENT AND SUBDIVISION

Extent of the Industry. — Stone production is the most widespread of
all industries in this country except agriculture, for rock deposits are
exploited in every State and in a great majority of the counties. In
the United States the average annual production of stone of all kinds,
including slate, from 1927 to 1931, was more than 176,500,000 short tons,
with an annual value exceeding $216,300,000. About 2,800 quarries and
mines are in operation, and the number of employees in them and in
directly associated plants is approximately 90,000.

Delivery of the enormous tonnage of stone to innumerable markets
is an important transportation item, involving rail, water, and truck
haulage. Coal and oil burned in quarries, mills, cement plants, and lime
kilns constitute an appreciable part of the fuel production of the country,
and the machinery and explosives used create an extensive market for
factory products. Thus, through its wide scope and complex ramifi-
cations stone holds a dominant place in the Nation's industry and exerts
a pronounced influence on national growth and development.

Major Divisions of the Industry. Dimension Stone. — The oldest use
of stone and the one that has become increasingly important through the
centuries is for building purposes. At first, rough walls were built of
scattered boulders, but with increasing knowledge of the use of tools
stone was quarried from solid ledges. Before the age of explosives and
before steam and compressed air were utilized quarrying was slow and
laborious; nevertheless, the pyramids and obelisks represent remarkable
engineering skill. These magnificent stone structures were built by
innumerable slaves, whose labor extended over many decades. Since
ancient times stone has been a favorite material for constructing the
finest buildings. Growth and development in art and architecture have
been expressed in noble structures, and we are indebted to the enduring
nature of stone for the preservation of many invaluable records of past
achievement.

The hewing of stone from its native beds with only the crudest hand
tools made it too costly for use, except in temples, palaces, and similar
structures. With the invention of explosives, the advent of steam power,
and, later, the use of electricity and compressed air, blocks of stone were
obtained with increasing ease, and rock became more and more widely
available as a building material. From cathedrals, bridges, and other

4 THE STONE INDUSTRIES

great public works it has found its way to smaller and less pretentious
structures, even to small one-family homes.

Dimension stone is used for other purposes than for building. In
ancient times a pile of stones was raised as a memorial, and from this
custom has developed the monument or headstone cut from suitable rock
and carved with a fitting inscription. Stone blocks are also used for pav-
ing streets and roads and for the manufacture of curbing. In addition,
stone has many special uses, such as for electrical switchboards and
blackboards.

Crushed Stone. — ^The use of crushed or broken stone developed much
later than that of dimension stone. Stone sledged by hand, usually by
convict labor, was used in road construction, and this use increased
rapidly. With the invention of cement and with mass production made
possible through explosives, power crushers, and screens the broken-stone
branch of the industry grew with phenomenal speed. In 1886 the output
of crushed and broken stone was smaller than that of dimension stone,
while in 1930 it was thirty times as great. Concrete aggregate, road
stone, and ballast are the principal products.

Stone Used in Manufacturing Processes. — For practically all the uses
mentioned above, stone is employed crude and untreated. It may be
shaped, polished, crushed, or ground, but its physical and chemical
properties remain essentially unchanged. In many modern industries,
however, stone undergoes physical and chemical changes, the final
product being quite different from the raw material in both form and
composition. Outstanding examples are limestones manufactured into
cement, lime, or calcium carbide; dolomite made into refractories; and
crushed sandstone fused with other products into glass.

Varieties of Stone Used. — The more common rocks used in com-
merce are granites and related igneous rocks, limestones, marbles, slates,
and sandstones. Soapstone also is included as a branch of the dimension-
stone industry. Many rocks in commercial use do not properly belong
to any of the foregoing groups. When employed as dimension stone
they usually are classed with one of the major groups; when used in
crushed or broken form they are considered a miscellaneous group.

CHAPTER II
MINERALS AND ROCKS

Distinction between Rock and Stone. — While the words "rock" and
"stone" are often regarded as synonyms, there is a definite distinction
in their meaning. The term "rock" is applied to a geologic formation
in its crude form as it exists in the earth. "Stone" is more properly
applied to individual blocks, masses, or fragments that have been broken
from their original massive ledges for application to commercial use.
Therefore, in chapter I the term "stone" is generally employed because
reference is made to manufactured products; in Chapter II "rock" is
used because the text relates to geologic formations as they exist in nature
before exploitation for economic use.

Relation of Rocks to Minerals. — To understand rocks properly one
should be acquainted with minerals, because rocks consist of them.
The relationship may be brought out most clearly by comparing minerals
with letters and rocks with words. Just as there is a word of one letter,
the article "a," so we have rocks made up essentially of a single mineral;
for example, limestone, which is the mineral calcite, or sandstone, a form
of quartz. Some words are made up of many letters, and in like manner
some rocks consist of several minerals; thus, granite consists of feldspar,
quartz, mica, and sometimes small quantities of hornblende, magnetite,
pyrite, garnet, and other minerals. A knowledge of rock-forming miner-
als is therefore a necessary preliminary to a well-balanced concept of
rocks. It may be mentioned, however, that some rocks consist wholly
or partly of natural glass or volcanic dust — materials that cannot properly
be classed as minerals.

Rock -forming Minerals. — It is assumed that the reader or student
who attempts to gain knowledge of the stone industries through these
pages has had at least an elementary course in mineralogy. Those who
lack this advantage or who desire to refresh their minds on the subject
are referred to textbooks or handbooks on mineralogy, because space will
not permit descriptions of minerals or means of their identification.

The important minerals in igneous rocks are feldspars, quartz, mica,
hornblende, and augite. Those most abundant in sedimentary rocks are
calcite, dolomite, and kaolinite (clay). Minor constituents include
chlorite, epidote, tremolite, actinolite, olivine, serpentine, garnet, sphene,
zircon, talc, pyrite, marcasite, magnetite, hematite, limonite, and
apatite.

6 ' THE STONE INDUSTRIES

Classification of Rocks. — Rocks are classified according to their origin
into three great groups — igneous, sedimentary, and metamorphic.
Igneous rocks are those that originated from molten masses or magmas
more recently regarded as high-temperature solutions. Semiliquid mag-
mas deep within the earth cool more or less slowly as they approach the
surface until a condition of solidification is attained. The nature of
the resulting rock depends on both the composition of the magma and the
rate of cooling. Magmas that cool very slowly at great depth tend to
form coarse-grained rocks, such as granites and gabbros, because slow
cooling ordinarily promotes coarse crystallization. On the other hand,
rapid-cooling magmas form fine-grained rocks, such as basalt and aplite.
Some rocks, consisting of relatively coarse crystals scattered throughout
a fine-grained ground mass, are known as the "porphyries."

Sedimentary rocks are sometimes referred to as "stratified," because
they are formed of sediments laid down in successive strata or layers.
The materials of which they are formed are derived from preexisting
rocks. Processes of rock decay or disintegration on the surface of the
earth, though very slow, are continuous and produce stupendous results
through centuries and geologic ages. Alternate frost and heat open
innumerable fractures in rocks; chemical agents of the atmosphere or of
surface and subterranean waters penetrate them and dissolve part of the
rocks. Rain, streams, waves, tides, and glaciers loosen the shattered
fragments, grind them up, and transport them far from their sources.
Wind, too, is an agent of erosion and transportation. . Millions of tons,
even cubic miles, of rock are disintegrated by these various agencies and
carried away to oceans, lakes, and river beds where they are deposited
as sediments. In addition to these products of rock decay, myriads of
organisms that inhabit the oceans or lakes secrete calcium carbonate or
silica from the water to form their shells, and their skeletal remains add
to the accumulations of rock-forming material. Thus, three great proc-
esses— rock disintegration, transportation, and redeposition — are now
and have been at work for ages. These processes — aided, as has been
stated, by organic agencies — have formed most of the sedimentary rocks.
Four major types are thus formed — conglomerate, sandstone, shale, and
limestone.

Metamorphism means change in form. Rocks of either igneous or
sedimentary origin that have been changed profoundly during the course
of their existence are known, therefore, as "metamorphic rocks." The
chief agencies that produce such changes are pressure, heat, and chemical
reaction. Rocks deep in the earth may become plastic under great pres-
sure and high temperature and by earth movement may be tilted or folded
into complex forms with a banded or schistose structure. Pressure may
cause recrystallization, and thermal waters may dissolve, transport, and
reprecipitate many minerals. Thus, new rocks may be formed of a

MINERALS AND ROCKS 7

texture and composition quite different from those of unaltered igneous
or sedimentary types.

The principal igneous rocks are granite, aplite, syenite, diorite, gabbro,
basalt, diabase, rhyolite, and tuff. Sandstone, conglomerate, shale,
limestone, and dolomite constitute the group of sedimentary rocks. The
metamorphic group includes gneiss, schist, quartzite, slate, marble, and
soapstone. Most of the above-named varieties are defined and described
in some detail in various following chapters devoted to discussion of their
distribution and exploitation. For those desiring a more thorough
treatise several textbooks on petrography are available.

General Distribution of Rocks in the United States. — As may be
inferred from the foregoing brief description of the origin of rocks, their
occurrence is directly related to the geologic history of each region.
The Appalachian district of eastern United States, extending from Maine
and Vermont to Georgia, is a rugged, mountainous region that has suffered
more or less extreme folding or metamorphism ; therefore, as one would
expect, metamorphic rocks, such as crystalline marbles, slates, gneisses,
and schists, are to be found there. Throughout the district many unal-
tered rock areas also occur and comprise important deposits of granite,
diabase, gabbro, sandstone, and limestone.

Between the Appalachian belt and the Rocky Mountains is a vast
area in which characteristic metamorphic rocks, such as marble, slate,
and gneiss, occur rarely because this is primarily a region of flat-lying
sediments that have been distorted very little by mountain-building
forces. Nearly horizontal limestone and sandstone beds are the charac-
teristic commercial rocks of the area comprising the eastern portions of
West Virginia, Kentucky, and Tennessee; all of Ohio, Indiana, Illinois,
Iowa, Nebraska, North and South Dakota, Kansas, Mississippi, Louisi-
ana, Florida, Oklahoma, southern Minnesota, Wisconsin, and Michigan;
and most of Missouri, Arkansas, and eastern Texas. Isolated areas of
granite occur in Wisconsin, Minnesota, Missouri, South Dakota, Arkan-
sas, Oklahoma, and eastern Texas.

West of the prairie country is another belt, the Rocky Mountain area,
in which the rocks are greatly crumpled and folded. Here again the
igneous and metamorphic rocks are abundant. This belt passes through
Idaho, Montana, Colorado, and New Mexico. Some of the granites,
gneisses, and marbles where accessible, have commercial importance.
From the Rocky Mountains to the Pacific Coast igneous rocks, of both
the granitic type and the more basic varieties such as basalt and gabbro,
are very common. Regional metamorphism has produced marbles and
slates, but many unaltered limestones and sandstones are found. Vul-
canism of comparatively recent geologic age characterizes much of this
great western area; and the resulting rocks, such as lava, rhyolite,
andesite, and volcanic tuff, are common. Such rocks are rarely found in
the Eastern or Central States.

CHAPTER III
FACTORS GOVERNING ROCK UTILIZATION

Rock Qualities on Which Use Depends. — Although rock is the most
abundant of all material things only a small fraction of the occurrences at
or near the earth's surface is fit for commerce. Requisite qualities which
are variable, depending upon the use to which the stone is to be applied,
are covered in following commodity chapters.

Importance of Other Factors Than Quality. — Although utilization
depends to a marked degree on physical or chemical adaptability, other
factors are equally important. Owners of rock deposits are prone to
assign too much importance to the quality of their materials without
adequate attention to certain economic factors that affect the success or
failure of any stone enterprise. For example, building-stone deposits of
most excellent quality would be valueless if situated in northern Alaska
because the cost of transportation to the nearest market would be
prohibitive.

Available Markets. — A study of market outlets for the type and
quality of stone available is essential to most successful operation. If the
quarry product is crushed stone or similar material that commands a low
price per ton, local markets are more important than those at a distance ;
favorable transportation, however, may extend the market range, which
is also influenced directly by production costs. A low-cost plant can
compete in a wider area than a high-cost plant handling the same class
of commodities. Present and probable future demand should be con-
sidered in relation to the production capacity of plants handling com-
petitive materials within the economic shipping radius. For relatively
high-priced products, such as ornamental granites and marbles, trans-
portation is a less formidable item in the total delivered price, and the
market range may be nationwide. A wide market area, however, brings
them into competition with all other similar materials ; successful market-
ing depends upon quality, workmanship, popularity with consumers,
prompt delivery, and aggressive salesmanship.

Diversification of Products. — Practically every quarry and pit can
produce a variety of grades and classes of materials, A slate quarry may
yield roofing slate, structural and electrical slate, blackboards, roofing
granules, and slate flour. A granite quarry may provide monumental
stone, cut stone, ashlar, rubble, paving blocks, curbing, and crushed stone.
Many operators tend to concentrate on one product and discard as waste

FACTORS GOVERNING ROCK UTILIZATION 9

any material that can not be applied to this particular use. For profitable
operation in a competitive market diversification of production is
desirable, and a market should be sought for all types of materials avail-
able in a quarry. Although a certain amount of waste is inevitable the
enormous piles of rejected stone in many quarry regions indicate that an
inquiry might profitably be conducted into the possibility of more
extended utilization of by-products.

Transportation Facilities. — Stone is heavy, and the haulage charge is a
considerable proportion of the delivered price; for the lower-priced
products it may be the chief item of cost at point of consumption.
Trucks now handle local delivery almost universally, and the cost
depends primarily on the nature of the roads. They are also being
employed to an ever-growing extent for distant delivery, the main
incentives being the increasing mileage of hard-surfaced roads and the
increasing speed of travel, as trucks carrying 6 to 8 tons now attain a
speed of 35 to 50 miles an hour.

For distant markets rail or water facilities are essential. Even
though the rock is of superior quality, deposits far from railroads may
have little value. Such markets are controlled largely by freight rates.
Wherever possible commodity rates should be established. Many
railroad companies prefer to haul stone because its imperishable nature
permits shipment in open cars.

Transportation by water is becoming increasingly important, as
indicated by the recent completion of a deep waterway on the Ohio River,
and the great increase in quantities of limestone, gypsum, and cement now
conveyed by this means. Attention may be directed to increasing
tonnages of limestone carried on the Great Lakes: 13,933,378 tons in
1927; 15,679,551 tons in 1928; and 16,269,612 tons in 1929. Water rates
are usually lower than rail rates.

Production Costs. — The success of any stone enterprise depends
largely on maintaining low production costs. High-cost plants can exist
in a competitive market only where some favorable circumstance, such as
superior quality of the stone, by-product utilization, effective sales
organization, or rapid delivery, gives them an advantage. Quarrymen
must therefore keep abreast of the times in efficiency of methods and
equipment. Today low cost depends primarily on plant mechanization.

Only by using some effective system of accounting can a knowledge
of costs be obtained. Hence systematized cost-keeping is to be regarded
as an important economic factor in conducting any stone enterprise.

Competitive Products. — Stone is meeting increasing competition
from metals and synthetic products. Aluminum is employed in place
of stone for both interior and exterior use. The movement toward all-
metal construction is attracting much attention, while glass, enameled
steel, and other ceramic products are finding new and important

10 THE STONE INDUSTRIES

uses. Alert stone producers are watching all such trends with exceeding
care.

Labor and Wages. — Usually the largest single item in production cost
is the amount paid in wages. Abundance or scarcity of labor, the
prevailing wage level, and living conditions have an important influence
on quarry methods. Scarcity of labor or abnormally high wages encour-
age more complete mechanization. Most stone producers recognize the
value of giving special attention to the health, safety, and comfort of their
workers, for by so doing they build up a personnel of steady employees, a
condition advantageous to both employer and laborer.

CHAPTER IV

PROSPECTING AND DEVELOPMENT
PROSPECTING

Development work should not be started on a deposit without
reasonable assurance of an available mass of rock sufficiently high in
quality and abundant in supply for profitable exploitation. Prospecting
is often found advantageous in quarries that have long been in operation ;
it is, in fact, a continuous activity with some companies, which enables
them to determine the extent of reserves and to plan future developments
intelligently.

If the rock appears in bare outcrop, usually a rough estimate of its
quality and extent can readily be made. Sedimentary rocks are, as a rule,
fairly constant in composition throughout the same bed or zone of
deposition, and the greatest variations are found in passing from one bed
to another; therefore, all beds that may be included in a quarry are
usually sampled. A cliff or escarpment along a stream or gulley is
especially valuable, because it provides a cross section which permits
tests of quality at various levels. If such a cross section is not available
in nature, test holes are drilled at such intervals as will supply adequate
data on the whole area under consideration.

The prospecting method is governed to some extent by the type of
operation. If the chemical composition of the rock is of primary impor-
tance, as in furnace flux, lime, or cement materials, churn-drill cuttings
will supply material for chemical analyses. Drill cuttings are sampled
at regular intervals, for example, every 5 feet, and an exact record is kept
of the drill hole and depth at which each sample is taken. The distance
between samples is governed by the uniformity of the rock. Where
analyses lack uniformity samples are taken at closely spaced points while
in rock of more constant composition they are obtained at wider intervals.

For dimension-stone and most crushed-stone uses the physical are
more important than the chemical properties of a rock. Dimension stone
must be free from cracks, of uniform texture, of attractive color, and for
some uses capable of taking a polish. For crushed-stone uses rock must
have satisfactory strength, soundness and low absorption. Churn-drill
samples can not be used for testing these qualities. Core drilling is
desirable because it not only provides data on the structure and extent
of the deposit, but this type of drill cuts out cylindrical masses suitable
for making physical tests. Diamond core drills which are in common

12 THE STONE INDUSTRIES

use, consist of a rotating steel drum with black diamonds (carbonados)
set in its lower edge. Some of the newer types of extremely hard alloys
are now being used as substitutes for diamonds in cutting softer rocks.
Shot drills also give satisfactory service; cutting is done with a rotating
steel drum fed with steel shot as an abrasive. Prospect-drill cores are
usually 3 inches, or smaller, in diameter.

The position and spacing of holes are governed by the nature of the
rock. Usually the geology of a region is studied thoroughly. General
information regarding the geology usually may be obtained from Federal
or State geological reports, although some companies employ trained
geologists to work out the structure and relationships of all rock forma-
tions associated with an operating or prospective quarry.

No definite rules can be given for the position or arrangement of holes.
In flat-lying beds of uniform thickness and fairly constant composition
they may be spaced at wide intervals — 100, 500, or 1,000 feet; where
rocks are folded or tilted, or where changes in composition or structure
occur within short distances, they should be spaced more closely.
Detailed maps are made for complex deposits. From a map constructed
after careful study of exposures the position, thickness, and slope of beds
may be determined with fair accuracy. In bedded deposits drill holes
usually are projected approximately at right angles to the bedding. To
intersect steeply dipping beds inclined drill holes may be required; for this
purpose a core drill has advantages over a churn drill, for it may be used
to drill holes at any angle, even in a horizontal position if so desired, while
except in rare instances churn-drill holes are vertical.

Accurate records of every drill hole are kept, and a map is made
showing its exact location. As each core section is removed it is marked,
recorded, and stored for future reference. Some large companies main-
tain fireproof storage sheds for prospect-drill cores.

The direct cost of sinking 5}^- to 6-inch churn-drill holes in limestone
is 20 to 60 cents a foot. These figures apply to constant drilling by
experienced workmen. Drilling harder rocks, such as trap rock and
granite, is more expensive, the cost ranging from $1.50 to $6.00 a foot.
Core drilling with shot or diamond drills costs $3.00 to $5.00 a foot,
depending on the nature of the rock and drilling conditions.

When the extent of a stone deposit is known, the approximate ton-
nage may easily be determined. Rocks vary somewhat in weight.
Merrill^ compiled tables of the weight of many building stones. The
average of 68 granites was 166 pounds per cubic foot; of 36 limestones,
dolomites, and marbles, 161 pounds; of 76 sandstones, 141 pounds;
and of 4 trap rocks, 182 pounds. Sandstones are the most variable
because they differ so much in porosity.

1 Merrill, G. P., Stones for Building and Decoration. 3d ed., John Wiley &
Sons, Inc., New York, 1910, pp. 498-507.

PROSPECTING AND DEVELOPMENT 13

To determine the approximate number of short tons available in a
limestone deposit the length, width, and depth in feet, as proved by-
prospect drilling or other methods, may be multiplied and this product
is then multiplied by the average weight per cubic foot (161 pounds)
and divided by 2,000. For granite or sandstone the corresponding figure
for weight per cubic foot may be substituted. Generally it is deemed
unwise to expend the large sum necessary to establish quarries and finish-
ing plants unless as a result of prospecting a reserve of good rock suflficient
for at least 20 years' operation is assured. Some companies operating
dimension-stone deposits open up quarries at moderate expense and sell
their products in rough blocks until the quality of the rock is proved,
marketability established, and a definite income assured. In due time
finishing mills may be built and equipped.

The determination of overburden is a phase of prospecting. Both
the depth and nature of overlying material, whether sand, gravel, clay,
or inferior rock, may be learned by drilling or trenching.

STRIPPING

Nature and Thickness of Overburden. — Stripping is the process of
removing the overburden of clay, gravel, or sand from the rock surface.
Many deposits of marketable rock are overlain with inferior quality rock,
which in a sense may be regarded as overburden. However, as methods
of removing solid rock, whether barren or useful, are quite distinct from
those employed in handling soil, removal of inferior waste rock is to be
classed as a quarrying rather than a stripping problem.

Most stone producers are interested in stripping. In certain places
quarries are worked in rock formations that appear in bare outcrop, and
fortunate owners of such quarries may view their neighbor's stripping
problems with a certain degree of complacence. Most commercial
rock deposits, however, are covered with varying depths of rock debris.
Indeed, the absence of all overburden is not always an unmixed blessing.
The writer has observed granite areas where 10 feet or more of soil has
preserved the rock almost to the surface, while other parts of the area
that were in bare outcrop were altered and discolored too greatly for
monumental use to depths of 4 to 8 feet. Removal of such rock as waste
is moreover more costly than removing several feet of soil.

The depth of overburden ranges from a few inches to 10, 20, 30, and
in exceptional instances even 40 or 50 feet. Likewise, the nature of mate-
rials composing it is variable. It may be easily disintegrated loam,
sticky plastic clay, sand, gravel, boulders, or even a hardpan that may
require blasting.

Stripping usually is a problem of greater magnitude in the crushed
than in dimension-stone industries. For crushed-stone uses a great
volume of stone must be handled; many quarries produce thousands of

14 THE STONE INDUSTRIES

tons a day. This great bulk of material demands rapid widening of
quarry walls, and stripping may become continuous. The dimension-
stone branches of the industry handle relatively higher-priced products
per ton which require much more labor in preparation, and the tonnage
produced is correspondingly lower. Working at much greater depths is
justified by the more valuable products, and 5 or 10 years may elapse
before a new pit is started or a new bench opened.

Clean Stripping. — For certain classes of quarries clean stripping is
essential; for others it is immaterial. Purity has first importance for
stone applied to chemical uses. Silica and alumina are most undesirable
impurities in limestone for lime manufacture and for furnace flux, and
such impurities are the chief constituents of the overburden. Clean
stripping is therefore essential at such quarries. On the other hand, in
the manufacture of portland cement clay is added to the limestone to
obtain a proper mixture; hence, if some clay is quarried with the rock
and proper care exercised in subsequent addition of clay, no detriment
to the product will ensue. Similarly, in dimension-stone production
surface debris will not harm the product ; it will be separated from quarry
blocks in due course and removed with other quarry waste. In best
quarry practice, however, as much of the overburden as can be handled
conveniently is removed before underlying rock is quarried.

Stripping Difficulties Due to Erosion Cavities. — Limestone and marble
are exceptionally difficult to strip because the slow erosion of circulating
water follows joints and cracks and thus wears away the rock surface
very irregularly, leaving numerous tortuous cavities filled with clay,
sand, or gravel. Generally the upper 10 or 20 feet consists of knobs or
pinnacles of rock standing in a mass of clay. Granites, sandstones, and
trap rocks are also subject to erosion, and quite irregular surfaces may
result; usually, however, they are comparatively smooth and regular.
Erosion cavities cause much difficulty and greatly increase the cost of
stripping.

Stripping Methods. — No quarry process is more variable than strip-
ping. The nature and depth of overburden and conditions of its removal
and disposal show wide differences from quarry to quarry. Therefore,
equipment and methods commonly employed are subject to similar
variations, which are discussed briefly in the following paragraphs.

Hydraulic Method.— The hydraulic method, which simply involves
washing the overburden away with a stream of water under pressure, is
the cheapest and most effective. Conditions for its successful use are,
however, somewhat exacting, the chief requirements being as follows:

1. An ample supply of water must be obtainable. An average of
about 10 tons of water is needed for each ton of overburden removed.
However, the same water may be used repeatedly if settling basins are
provided for clarification.

PROSPECTING AND DEVELOPMENT

2. A favorably situated waste-disposal area is essential. The best
conditions exist where the soil may be washed back from the quarry face
or laterally into ravines or basins where it may remain.

3. Hydraulicing is effective only where the overburden is friable
enough to be washed down and carried away with a stream of water.
The presence of hardpan or of numerous heavy boulders may cause great
difficulty and justify the use of other methods.

The equipment required for hydraulic stripping includes a pump, a
pipe line, a mounted nozzle or monitor, and possibly an additional
dredging pump, together with the necessary source of power. A great
advantage of the hydraulic method is the wide range of action and ease of
moving from one point to another. Its adaptability for removing clay
and sand from irregularly eroded surfaces is an outstanding advantage.

1 I . 1 A rugged ruck builaet stripped b> the hj draulic method.

Soil that could be removed only with great difficulty by other means is
washed out by the stream of water directed into pockets and cavities.
This means is therefore particularly adaptable for stripping limestone or
marble deposits. Figure 1 shows a typical eroded limestone surface
from which practically all soil has been washed away by this method.

Hydraulic stripping is a potent source of stream turbidity which may
be detrimental to other interests. This drawback may be overcome by
establishing wide settling basins.

The cost of hydraulic stripping is quite variable but usually very low.
Costs range from less than 1 cent to 12 cents a cubic yard in quarries in
different parts of the country.

Dragline Scraper or Excavator. — Where a convenient dumping ground
is available a dragline scraper is effective. It lacks flexibility in lateral
movement, however, unless provided with special attachments; if worked

16 THE STONE INDUSTRIES

from a derrick arm it is much more flexible, as the entire equipment is on a
portable mounting, and the lateral motion of the derrick arm gives the
excavator a wide range of action. Draglines have been used successfully
in cleaning out large erosion cavities filled with clay.

Power Shovel. — The power shovel is the most popular type of stripping
equipment. Steam and electric shovels are in common use, and com-
pressed-air shovels are employed in a few localities. Power shovels
handle material of all kinds with great facility but are not well-adapted
for work on uneven rock surfaces. For removing clay from the larger
erosion cavities some of the smaller types of tractor or caterpillar shovels
with dippers not more than three-fourths yard in size are used. Various
methods have been tested to overcome successfully the difficulty of
stripping rough, eroded limestone surfaces with a power shovel. As
they are encountered rock projections may be broken by blasting and
set to one side or thrown over the edge of a quarry by means of the shovel
dipper; better access to the soil is thus provided. Another method is to
blast and load rock and soil together, but unless a washer is used clean
separation later is difficult.

Costs of power-shovel stripping vary greatly according to conditions.
A thick overburden of easily excavated soil on a smooth rock surface may
be loaded and removed to a near-by dump for only 15 to 30 cents per
cubic yard. Under average conditions the cost runs from 30 to 50 cents
a cubic yard, but where loading is difficult it may be considerably higher.

Other Mechanical Equipment. — For cleaning out deep erosion cavities
clamshell buckets worked from derrick arms have limited application.
Small tractor excavators similar to those for road grading are also
employed. Where the overburden is moved only a short distance
mechanical conveyors are used. Scrapers with or without wheels, hauled
by horses or mules, are employed where the overburden is too thin for
successful power-shovel operation. Various methods may be combined,
as, for example, a dragline scraper which dumps through a trap in a
platform into cars that are hauled by locomotives.

Hand Methods. — Removal of overburden by hand methods, involving
the use of picks and shovels by quarry workers, is slow and laborious.
Under modern wage conditions it is also costly. Dirt loading by hand at
quarry floors is often done by contract at 15 to 25 cents a cubic yard,
but the dirt is loose and easily loaded. Loosening and loading undis-
turbed soil may cost 30 to 45 cents a cubic yard, and a haulage charge
must also be added. Clay dug from deep pits and cavities by hand may
require several handlings and the cost is increased proportionally.

Utilization of Overburden. — At some cement-plant quarries clay
which overlies the limestone may be one of the necessary raw materials;
otherwise, it is rarely used except as a filling material. In the latter
capacity it may be employed to fill swamps, ravines, or other low places.

PROSPECTING AND DEVELOPMENT 17

rendering such areas available for agriculture or building. Overburden
may also be used for dams, roadways, or railroad grading. In rare
instances clay overburden is suitable for brick.

Disposal of Overburden. — Proper disposal of material stripped from
rock surfaces requires keen judgment and foresight. Desire to attain
quick results at small expense and lack of foresight regarding probable
extent of future operations are the chief causes of removing soil to an
insufficient distance from the excavation, a common mistake in stripping.
In quarrying dimension stone a large amount of waste usually is added
to the pile of overburden, and in the course of years the accumulation
may be very extensive. Consequently, after a few years' operation
quarry owners find it necessary to handle waste a second time, augment-
ing greatly the expense of quarrying. If excavations are too close to
spoil banks, as quarries are gradually enlarged rock slides may result;
some quarries have been abandoned on this account.

As important as distance is the direction in which waste is carried.
If prospecting has been adequate the direction future development must
take usually can be determined. Thus, if workable beds are narrow and
steeply inclined, obviously lateral development must follow the direction
of strike; nevertheless, in many quarry regions waste has been piled
directly over good rock that would in the natural course of events be
quarried in a few years. Thus, extension of workings is impeded or
made more costly.

Provision for adequate disposal of waste is therefore an important
part of every quarry plan. It may, indeed, be found necessary to carry
waste a considerable distance, in which event an efficient transportation
system is essential. Overburden and waste are at times thrown into
abandoned quarries, but before this is done an operator should be assured
that permanent abandonment is fully justified.

Avoidance of Stripping by Underground Mining. — By adopting under-
ground mining methods the stripping problem is sometimes effectively
solved. An unusually heavy overburden is one of the chief incentives for
undertaking excavation of rock by means of drifts and tunnels, for this
method eliminates stripping costs.

GENERAL METHODS OF OPERATION

Open-pit Quarrying. — Most rock products of commerce are obtained
from open quarries. Material suitable for use ordinarily is found at or
near the surface of the earth, and the most economical method of working
is to open up a face of the rock ledge. As rock is separated by blasting or
other means, an opening is gradually enlarged and deepened, its size and
shape depending greatly on the rock structures. Wide, shallow openings
may be made in comparatively thin flat-lying beds, such as are common
in limestone districts of the Middle West. Where beds are folded and

18 THE STONE INDUSTRIES

tilted at high angles, as in the Appalachian region of the Eastern States,
open pits may be narrow and deep. Some open-pit slate quarries of
Pennsylvania have reached depths of 500 to 700 feet because the desirable
beds are relatively narrow and almost vertical. Also, where land values
are high, and property lines restricted, or where a heavy overburden of
soil or waste rock makes lateral extension expensive, quarries are likely
to be narrow and deep.

There are two types of quarries, the "shelf" quarry and the "pit"
quarry. Sometimes a ledge of serviceable rock stands above the level
of the surrounding country, and by working into the hillside a quarry
can be developed, with the floor little if any lower than the surrounding
land surface. Such ready access and easy transportation are advan-
tageous. Furthermore, drainage is usually automatic, and pumping
expense is avoided. Excavations of the shelf-quarry type can usually be
classed as low-cost operations.

Conditions are not always so favorable; a rock deposit may not
extend above the general level, and a pit must be sunk. Access is gained
by ladders, stairs, or mechanical hoists, and material is transported from
the quarry by inclined tracks, derricks, cableway hoists, or other means.
Such pit quarries also require pumping. Though less advantageous than
shelf quarries, thousands are in regular operation. When properly
designed and well-equipped they may be operated at a cost which
compares favorably with that at many shelf quarries.

Underground Mining. — When quarrying of rock first was begun as an
industry, excavations were made in formations readily available at the
surface of the earth. Through long years of continued operation the
most available outcrops were gradually worked away, and quarries
reached increasing depths. Many limestone beds which provide suitable
stone dip at steep angles and are of limited thickness. In following these
beds down the dip greatly increasing depths of overburden are encoun-
tered. Consequently, in many localities mounting difficulties in the
way of open-pit quarrying, with rising costs, have induced operators to
change their systems of excavating and to develop underground mining
methods. Many limestone and marble, and a few granite and slate
deposits, are successfully mined underground. Selective mining can best
be accomplished by the underground method, for drifts and tunnels
may be confined to serviceable rock, waste and overburden being left
undisturbed. As workmen are not exposed to the weather, working
conditions are also more favorable.

Gloryhole Mining. — Gloryhole mining is adapted only to the produc-
tion of broken stone. This method has features in common with both
open-pit and underground mining, and is modified to suit varying condi-
tions. A circular or oblong open pit is the most usual type. Rock
is quarried around the sides and conveyed by dragline or other means

PROSPECTING AND DEVELOPMENT 19

to a funnel-shaped opening at the center, where a chute is provided
through which the rock is conducted to cars which convey it to the
surface through a tunnel.

Bibliography

The following bibliography contains references to a few important articles that
have appeared during recent years on prospecting and stripping.
Armstrong, W. D. Hydraulic Removal of Overburden from a Stone Quarry.

Cement, Mill, and Quarry, vol. 27, no. 2, 1925, p. 35.
Bowles, OLrvER. Stripping Methods at Pits and Quarries. Pit and Quarry, vol. 8,

no. 3, 1923, p. 108.

Stripping Clay from Seams and Pockets in the Shenandoah Valley of

Virginia. Rock Products, vol. 26, no. 5, 1923, p. 53.

Stripping a Stone Quarry. Cement, Mill, and Quarry, vol. 33, no. 3, 1928,

pp. 6-14.
Engineering and Mining Journal. Finding New Mines. Vol. 116, 1923, p. 573.

Selling a prospect. Vol. 123, 1927, p. 2.

Hauer, D. J. Developing a Quarry. Pit and Quarry, vol. 9, no. 1, 1924, p. 61.
Massey, G. B. Hydraulic Stripping. Pit and Quarry, vol. 10, no. 10, 1925, p. 77.
MiLKowsKi, V. J. Hydraulic Stripping of Quarry Overburden. Rock Products,

vol. 26, no. 5, 1923, p. 51.
Pit and Quarry. Top Soil Removed by Two Clever Excavating Schemes. Vol. 8,

no. 5, 1924, p. 112.

Hydraulic Stripping of Overburden. Vol. 12, no. 3, 1926, p. 85.

When to Strip Overburden. Vol. 12, no. 11, 1926, p. 93.

Hydraulic Stripping in the Indiana Limestone District. Vol. 14, no. 10,

1927, p. 77.

Rock Products. Round-Table Discussion of Quarry Operation; Quarry Stripping.

Vol. 27, no. 5, 1924, p. 78.
Rush, D. B. Exploration and Geological Examination of a Quarry Property and

Their Relation to Financing. Rock Products, vol. 27, no. 5, 1924, p. 56.
Stone, R. W. What State Geological Surveys Are Doing for Rock Products, Rock

Products, vol. 27, no. 4, 1924, p. 27.

PART II
DIMENSION STONE

CHAPTER V

GENERAL FEATURES OF DIMENSION -STONE INDUSTRIES

DEFINITION OF DIMENSION STONE

The term ''dimension stone" is generally applied to masses of stone
prepared for use in the form of blocks of specified shapes and usually of
specified sizes. Other forms that find commercial use are designated
"broken," "crushed," or "pulverized" stone. Stone fragments that
are classed in the second group may be of specified sizes, the sizing usually
being accomplished by screening, but the outstanding distinction between
fragments of broken or crushed stone and masses of dimension stone is
that the former are irregular and are in an infinite variety of forms,
while the latter are cut to definite shapes such as rectangular, columnar,
tabular, or wedge-shaped.

PRINCIPAL USES

Building Stone. — One of the chief uses of dimension stone is as a
material of construction, but this branch of the industry contains many
subdivisions. In its broader sense the term "building stone" includes
stone in any form that constitutes a part of a structure; however, cut or
rough-hewn blocks for exterior w^alls are most widely used. They may
be employed only for certain parts, as for window sills, trim, cornice,
base courses, chimneys, or steps.

Cut stone is employed extensively for both interior and exterior
columns. The more ornamental types are utilized for interiors,
as floor tiles, steps, wainscoting, fireplaces, hearths, mantels, baseboards,
banisters, toilet inclosures, laundry tubs, and in various other ways.
Slabs are used for flagging. Cut stone is also in demand for bridges,
dams, retaining walls, docks, sea walls, lighthouses, and similar structures
where strength, permanence, and resistance to shock are essential.

Building stone used in the construction of walls is of four main types —
cut or finished stone, ashlar, rough building stone, and rubble. Cut
or finished stone is the most costly because, for the most part, blocks
are accurately shaped in accordance with detailed drawings. They
may be plain rectangular blocks for uninterrupted walls or cut and
carved to special shapes and designs for corners, window and door
spaces, caps, or cornices. This classification includes sawed limestone
and marble, finished or semifinished.

THE STONE INDUSTRIES

"Ashlar" is a term applied in general to small rectangular blocks
of stone having sawed, planed, or rock-face surfaces, contrasted with
cut blocks which are accurately sized and surface-tooled. Many types
are in use. Even-course ashlar consists of blocks of uniform height for
each course, although succeeding courses may be of thicker or thinner
blocks. They may be of uniform or of random length. Exceptionally,
end joints are slanting or irregular. Random ashlar consists of blocks

Fig. 2. — Ashlar in two-unit heights.

^ n ^^-

■Ar

Fig. 3.

-A common method of laying ashlar in three-unit heights.
Limestone Company.)

(Courtesy of Indiana

of several sizes that may be fitted together to make a wall having irregular
and unequally spaced joints. Two, three, or more unit heights may be
employed, as several smaller sizes may give the same height as one of the
larger blocks. Thus, as shown in figure 2, the two smaller blocks with a
mortar space between reach the same height as the larger block. In
figure 3 the use of random ashlar in three-unit heights is shown. It
may be observed from this figure that blocks which fit together properly
with 3^^-inch motor joints must have thicknesses of 4, 8)^, and 13 inches,
respectively. Random ashlar not only provides builders with means
of attaining remarkable variety in architectural design but permits
quarry and mill operators to utilize fragments of various sizes that

GENERAL FEATURES OF DIMENSION-STONE INDUSTRIES 25

might otherwise be wasted. The building of random ashlar walls is
mason's work, while the setting of cut stone is a separate art.
^ Rough building stone consists of rock-faced masses of various shapes
and sizes. Stone masons build them into walls having irregular joints.
They are widely used in residential construction for chimneys, basements,
or entire walls, and also to some extent for public buildings, bridges,
fences, and the more ornamental types of retaining walls.

Rubble is the crudest form of building stone. The term is generally
applied to irregular fragments having one good face. Such rock was once
in ordinary use for basement walls, retaining walls, or similar types
of construction for which concrete is now generally employed. Produc-
tion of rubble has declined greatly during recent years.

Monumental Stone. — Memorials range from simple markers and
headstones to elaborate and massive monuments. Usually stone that
takes a good polish is requisite; in fact, the very highest types of flawless,
uniform stone are used for monumental purposes. However, monuments
with tooled, hammered, or even rough-hewn surfaces are not unusual,
and less flawless stone may be thus employed.

No sharp line can be drawn between monumental and building stone,
for monuments merge into buildings. The Washington Monument is
essentially a building equipped with an elevator for passenger service,
though in design and purpose it is a monument. The Lincoln Memorial,
the Arlington Amphitheater, the Bok Singing Tower, and mausoleums in
various parts of the country are other memorials that have many features
of buildings and for which building stone is used.

Paving Stone. — One of the early uses of stone was for street and high-
way paving, the old Roman roads of Britain being outstanding examples.
While the demands for hard-surfaced roads were not so urgent long ago as
today, there was real need for something better than dirt or even broken-
stone roadways, particularly for the heavy traffic of growing cities.
Concrete was unknown, and blocks of native stone were the logical
materials. "Cobblestones" — rounded or irregular blocks — were widely
used but were gradually replaced by rectangular paving blocks with
smooth, even surfaces. During recent years concrete and macadam have
far outstripped paving blocks for hard-surfaced road construction, but
many stone pavements still give unsurpassed service under the most
severe traffic demands. They are found chiefly in railroad freight yards,
around docks, and in streets traversed by many heavy drays and trucks.
Paving blocks are also much in use between street-car tracks, not only
because of their wearing qualities but because of the facility with which
they may be taken up and replaced when track repairs are necessary.

Although the softer types of paving stones are gradually disappearing
with heavy traffic increasing year by year, granite and indurated sand-
stone, the most resistant types, are still in wide and steady demand.

26 THE STONE INDUSTRIES

Curbing. — The manufacture of curbing is an important branch of the
stone industry. Curbstones are of two types — straight and corner.
Corner curbs are curved; they are more difficult to make than straight
curbstones and require more material, as a considerable amount of rock
is wasted in shaping them. The harder stones are more durable than
concrete and on this account are particularly well-adapted for corner
curbs where shocks from the wheels of traffic are exceptionally destructive.

Flagging. — Flagging is used chiefly for sidewalks and for paving
courts, landings, and platforms, but the advantages of concrete for such
uses have led to a rapid decline in output. In the past probably 95 per
cent of the total flagstones produced were of bluestone, a variety of
sandstone. Ornamental slate flagging is now used quite extensively
and limestone, granite, and trap rock to a limited extent.

Miscellaneous Uses. — Stone is utilized in a multitude of minor ways
that may not be included in any of the above groups. In household
equipment it is found as radiator covers, table and dresser tops, lamp
bases, vats, sinks, refrigerator shelves, and flour bins. Ornamental
types are used for novelties, such as ink w^ells, paper weights, smoking
sets, ash trays, clocks, and statuary. Slate is used for blackboards,
bulletin boards, and billiard-table tops. Several types of stone are
widely used for electrical panels and switchboards. In yards, gardens,
and parks stone is employed for walks, stepping stones, statuary, foun-
tains, bird baths, and garden seats.

REQUISITE QUALITIES OF DIMENSION STONE

General Requirements. — Although innumerable occurrences of rock
are to be found throughout the world only a small part of them consist of
rock that will satisfy the exacting requirements of dimension stone.
Freedom from cracks and lines of weakness is essential. No deposit
that has irregular or closely spaced joints is suitable, because sound
blocks of moderate to large size are demanded. Uniform texture and
grain size, together with a constant and attractive color, are usually
required. The rock must also be free from minerals that may cause
deterioration or staining.

Another important quality is the state of aggregation. If the grains
are loosely coherent the rock may be described as "earthy" or "friable."
Rock in which the grains adhere closely and strongly is the most desirable.
However, when cementation is carried to an extreme as in the case of
some quartzites, the rock is very difficult and expensive to work. Some
important qualities that demand consideration are discussed in the
following paragraphs.

Composition. — A rock consists of one or more minerals made up of
elements combined in definite proportions, which may be determined by
chemical analysis, and the minerals may be determined by visual observa-

GENERAL FEATURES OF DIMENSION-STONE INDUSTRIES 27

tion with the unaided eye or with the assistance of a hand lens or micro-
scope. Often the value of a chemical analysis of dimension stone is
overemphasized, as adaptation to use depends chiefly on physical
properties. At times an analysis may have value; for example, it may
indicate the amount of clay in a limestone, a fact which has some bearing
on its durability. Usually study with a petrographic microscope is
much more effective than chemical investigation; it is also quicker and
cheaper. One skilled in the use of a microscope may identify the minerals
in a rock and note their state of aggregation, freshness, relative abundance,
impurities, and texture and to some extent interpret the history of the
rock and learn what influences have been at work to improve or impair
it for structural or other uses.

Hardness and Workability. — The hardness of a rock is its resistance
to abrasion and depends directly on the hardness and texture of its
component minerals. Most of the constituents of granite are as hard as
or harder than steel, and such rock is therefore difficult to tool. Pure
limestones are soft enough to be scratched easily with a knife. Marbles
are somewhat harder than limestones. The grains of a sandstone consist
of quartz, which is very hard, but workability depends rather on the
nature of the cementing material and its state of aggregation. A friable
sandstone may be worked readily because the grains separate with ease,
while a siliceous sandstone or quartzite, in which they are firmly cemented
together with quartz, is very difficult to cut and dress.

Hardness has direct bearing on the workability of all rocks, yet its
effect on use is quite variable. For exterior or interior walls or for
decorative effects the hardness of a rock is unimportant, in so far as
quality is concerned, because it is not subjected to wear. On the other
hand, for floor tile or stair treads hardness is very important, as the rock
is subjected to severe abrasion. It is the most essential quality of stone
used for paving and curbing, for such stone must be able to resist
adequately the abrasive action of heavy traffic.

Texture. — The term "texture" as applied to rock means size, degree of
uniformity, and arrangement of its constituent mineral grains. In the
rougher types of building stone uniformity is not required; in fact, recent
architectural demands tend toward variable, uneven texture. In the
more ornamental types of building and monumental stone uniform
texture has vital importance.

Qolor. — Rocks are of many colors, and choice depends on individual
taste or "prevailing fashion. Choice of color in stone is influenced by
location. For smoky cities white and very light colors are undesirable.
Some rocks change in color with age, but this is not always objection-
able. Practically all colors are in demand for monumental stone,
and those rocks in which there is marked contrast between polished and
tooled surfaces are preferred, for on such monuments inscriptions are

28 THE STONE INDUSTRIES

most easily read. For building stone, red, brown, buff, gray, or white
rocks are widely employed. Dark-gray or black rocks are in demand
only for certain special uses. The buff or yellow tints of many limestones
and sandstones and the red or pink coloration of many granites are due
to the presence of minute grains of iron oxides, but these are stable minerals
that cause no stains. Surface stains are serious blemishes and are
generally due to the presence of small grains of pyrite, marcasite, or
siderite which oxidize by weathering. Stains sometimes are caused by
cementing materials used in setting the stone.

Strength. — Rock is a very strong material. Structural stone that is
sound and suitable in other respects is almost invariably strong enough
for any use. Bridge piers, arches, and the bases of tall monuments must
sustain great pressure, but even in such structures the strength of ordinary
stone far exceeds the requirements of safety. The pressure on the base
course of the Washington Monument is less than 700 pounds a square
inch; and high-grade granites, limestones, and marbles will sustain a
crushing load of 10,000 to 25,000 pounds a square inch. Recent tests
at the United States Bureau of Standards on samples of Montana
quartzite indicated the remarkably high compressive strength of 63,000
pounds a square inch. A structure of such material would have to be
over 10 miles high before failure would occur from crushing of the lower
courses. It is, however, generally conceded that rock disintegrates and
tends to weaken more readily when under severe stress ; therefore a factor
of safety of 20 is usually demanded — that is, stone must be able to resist a
crushing stress twenty times as great as that to which it will be subjected
when placed in a wall. For ordinary uses, a stone that will sustain a
crushing strength of 5,000 pounds to the square inch is considered
satisfactory.

Tests of transverse strength — strength required to sustain a load
applied at the middle of a bar of stone supported at the ends — are more
important than crushing-strength tests, for they show the adaptabil-
ity of the stone for use as window and door caps.

Porosity. — Pore space or porosity, expressed as the percentage of pore
space to the total rock volume, is quite variable in different types of rock.
Sandstones may have a porosity of 1 to 10 per cent. Commercial
limestones range from less than 0.5 to 5 per cent. Marbles, granites,
and slates are usually of very low porosity, many of them less than one-
tenth of 1 per cent. Porosity affects the durability of stone by permitting
infiltration of water which may contain solvents, or which may freeze in
the pores. Early writers have stated that danger from frost action is
directly proportional to the percentage of pore space, but Buckley^ has
pointed out that the important factor to consider is the facility with which

^ Buckley, E. R., The Building and Ornamental Stones of Wisconsin. Wisconsin
Geol. and Nat. Hist. Survey Bull. 4, Econ. Ser. 2, 1898, p. 22.

GENERAL FEATURES OF DIMENSION-STONE INDUSTRIES 29

the stone gives up water. Rocks having pores of subcapillary size give
up their included water much more slowly than those with larger pores,
therefore those with fine pores suffer most seriously from frost action.
Parks^ determined the permeability of many rocks and found that it
bore no relation to the percentage of porosity or to the effect of frost.
It is apparent, however, that the solvent effect will be greater in rocks of
greater permeability. The extent to which a stone will take up water is
usually expressed as ratio of absorption, which is the proportion of the
weight of absorbed water to the weight of the dry sample.

Specific Gravity and Weight per Cubic Foot. — The specific gravity
of a stone is its weight compared with the weight of an equal volume of
water. It may be expressed in two ways — as "apparent" or as "true"
specific gravity. Apparent specific gravity is that obtained when pore
spaces are filled with air throughout the determination. True specific
gravity is obtained when pore spaces are eliminated, either by so com-
pletely saturating the rock that they are filled with water or by using
finely ground rock powder in making the determination.

The specific gravity of common rocks ranges from 2.2 to 2.8 and the
weight per cubic foot from 140 to 180 pounds, depending upon the weight
and relative abundance of the constituent minerals and upon the porosity.

Data on Physical Properties. — Merrill* presents numerous tables
showing specific gravity, strength, weight per cubic foot, ratio of absorp-
tion, chemical composition, and other properties of many building stones.
Since that book was written many thousands of tests have been made
and the results recorded. The United States Bureau of Standards has
made the most noteworthy contributions to our knowledge of the physical
properties of building stones. Publications^ covering marbles, lime-
stones, and slates are now available. Dale's various reports on marble,
granite, and slate as recorded in the bibliographies of the respective
chapters in this volume, also contain a great deal of physical test data.
Numerous textbooks and State reports also present tables or incidental
information on crushing and transverse strength, ratio of absorption,
weight, and other physical properties of stones from innumerable specific
localities. A compilation of this great mass of data would constitute

^. Parks, W. A., Report on the Building and Ornamental Stones of Canada. Can-
ada Dept. Mines, vol. 1, pt. 1, 1912, p. 62.

* Merrill, G. P., Stones for Building and Decoration. 3d ed., John Wiley & Sons,
Inc., New York, 1910, pp. 497-579.

^ Kessler, D. W., Physical and Chemical Tests on the Commercial Marbles of the
United States. U. S. Bur. of Standards Tech. Paper 123, 1919, 54 pp.

Kessler, D. W. and Sligh, W. H., Physical Properties of the Principal Commercial
Limestones Used for Building Construction in the United States. U. S. Bur. of
Standards Tech. Paper 349, 1927, 94 pp.

Kessler, D. W., Physical Properties and Weathering Characteristics of Slate.
U. S. Bur. of Standards Research Paper 447, 1932, 35 pp.

30 THE STONE INDUSTRIES

a book in itself, and lack of space forbids its presentation herein. There-
fore, the reader who desires knowledge of the qualities of stones from,
certain locations is referred to the texts mentioned in the footnotes or
given in the appropriate bibliographies.

Durability. — Climate has a very definite bearing on the durability
of stone. Cleopatra's Needle, a column of granite which was transported
to New York and set up in Central Park, is said to have suffered more
from exposure during a score of winters in the climate of America than
during the centuries it stood in the mild, uniform climate of Egypt.
Probably incipient decay had begun before its removal, and the severe
climate of this country speedily made the deterioration apparent.

Most standard commercial types of building and ornamental stones
are sufficiently durable for ordinary use. By examining the effects of
weathering on outcrops that have long been exposed to the elements in
undeveloped deposits the durability of rock may be judged, or where
stone has been quarried for many years observations may be made on
old structures in which it was used. In this respect America does not
have the advantages of the Old World, for even our oldest buildings are
comparatively new when considered on the basis of the life of high-grade
stone.

Durability of stone is now tested quite extensively in laboratories,
chiefly by means of accelerated freezing and thawing tests and by accel-
erated acid tests. Resistance to fire is an important consideration. It
has been found that limestones withstand the effects of fire up to the
point of calcination better than other stones. Next in order are sand-
stones, fine-grained crystalline rocks, and the coarser crystalline rocks.
As a rule, the finer grained and more compact the stone and the simpler
its mineral composition the better it will resist damaging effects of
extreme heat or the spalling effects that result from rapid cooling when
water is applied.

More detailed requirements for specific uses will be included under
the discussion of each commodity.

ADAPTATIONS OF RAW MATERIAL TO USE

Stone is employed in many different ways. Obviously the require-
ments of use are variable. Stone products differ from synthetic com-
pounds in that the composition and properties of the latter can within
certain limits be changed at will, whereas the composition and physical
character of stone remain exactly the same in the finished material as in
the solid rock ledge. Man can fashion rock into any desired size or shape
and can polish or otherwise finish the surface, but he is powerless to
change in the slightest degree the texture, inherent color, hardness, or
proportion or character of constituent minerals. He has, however, the
power of selection, and this must be exercised with great care. The

GENERAL FEATURES OF DIMENSION-STONE INDUSTRIES 31

stoneworker must study his material, be familiar with its properties,
and understand the requirements of use. He is thus enabled to judge
the possibilities of a rock deposit and its adaptations. Some rocks
are eminently fitted for monumental uses, some for building, and others
for interior decoration.

COMPLEXITIES IN MARKETING

Some quarrymen simplify their marketing problems by selling prod-
ucts in rough-block form to dealers or manufacturers. Rough blocks,
however, command a much lower price than finished products, and the
desire for larger incomes and increased profits has led many operators
to establish mills of their own. If structural stone is manufactured
marketing may become complex. Some quarries specialize in one
product, the marketing of which may be simple. While, as previously
shown, diversification has its advantages, marketing becomes more
complex because the various products may enter entirely different fields
of utilization. Large quantities of granite, limestone, and sandstone
are sold as rough blocks to independent mills, but slate is usually manu-
factured in plants directly associated with quarries.

ROYALTIES

Stone deposits are sometimes owned by one individual or company
and operated by an independent concern. Such properties are usually
worked on a royalty basis. Factors to be considered for the most
reasonable determination of royalty are the value of the deposit and the
quantity of commercially available material therein. Thus a fair market
value for the property, divided by the number of tons or number of
cubic feet of rock available, will give a fair figure for royalty.

The value of rock in the ground is commonly overestimated, for it
really constitutes only a small part of the selling price of the finished
product. A fair market value is often difficult to determine. It may be
defined as the value agreed upon between a willing seller and a prudent
purchaser, both of whom have enlightened understanding of the com-
modity involved.

Royalty is commonly expressed as a percentage of the selling price
at the mine or quarry. According to the Leasing Act of June 30, 1919, as
amended December 16, 1926, a minimum royalty of 5 per cent of the
net value of the output at the mine is charged for minerals taken from
Government lands. The royalty may exceed 5 per cent, the exact figure
being determined from a review of all the circumstances surrounding
each individual commodity or deposit.

Whatever the basis of determination, royalty is usually charged as
so much a ton or cubic foot of material sold. Royalties vary considerably
depending upon size of operation, value of product, and other factors. In

32 THE STONE INDUSTRIES

the Atlanta (Ga.) district, a royalty of 25 cents a cubic foot of block
granite and 2 to 5 cents a cubic foot of granite curbing is customary.
For Indiana limestone sold as cut stone, commanding a price of $2 or S3
a cubic foot, royalties ordinarily range from 4 to 10 cents a cubic foot.
If the limestone is sold as rough building stone the royalty is lower and
may be 2 to 5 cents a cubic foot. Royalties on slate are commonly about
10 per cent of the net selling price. A minimum average daily or monthly
production is usually a condition of a royalty agreement.

CHAPTER VI

LIMESTONE

DEFINITION

Limestone is a rock consisting essentially of calcium carbonate
(CaCOs), the mineral calcite. Rocks classed commercially as limestones
may contain varying quantities of magnesium carbonate; when 10 per
cent or more is present they are termed "magnesian" or "dolomitic"
limestones; if the amount approaches 45 per cent the rock is composed
essentially of the double carbonate of lime and magnesia (CaCOs,
MgCOs), the mineral dolomite. When used as dimension stone dolomite
is classed commercially as limestone.

ORIGIN

As pointed out in a preceding discussion of sedimentary rocks,
limestones have originated chiefly from calcareous organic remains,
supplemented to some extent by chemical precipitation. Only those
limestones that have been firmly consolidated have importance as
dimension stone.

PHYSICAL PROPERTIES

Limestones vary greatly in physical characteristics. Hardness
depends on the degree of consolidation as well as on the actual hardness
of the component minerals, but even the densest forms of limestone can
be easily scratched with a knife. They range from pure white to black,
the color effects being brought about chiefly by impurities. In texture
they may be amorphous, semicrystalline, or crystalline. They vary in
compactness from loosely consolidated marls through the denser chalks
to compact normal limestones and the harder marbles. The less-compact
limestones have the higher degree of porosity and may weigh as little as
110 pounds per cubic foot, whereas the more compact varieties may
weigh 150 to 170 pounds. For most uses dense, highly consolidated
forms are preferred.

VARIETIES

Limestones are classified according to the nature of their impurities.
"Siliceous" or "cherty" limestone contains considerable silica and
"argillaceous" limestone clay or shale. The so-called "cement rock,"
which is widely used for cement manufacture in the Lehigh Valley district
of Pennsylvania, is a good example of the latter. A "ferruginous"

34 THE STONE INDUSTRIES

limestone contains iron, which usually gives rock a buff, reddish, or
yellowish color; the "carbonaceous" or "bituminous" type contains
carbonaceous matter, such as peat or other organic materials.

Another series of names is applied to limestones, according to their
texture, state of aggregation, or appearance. "Common compact"
limestone, the most widespread type, consists of a fine-grained, dense,
homogeneous aggregate ranging from light gray to almost black. "Lith-
ographic" limestone is an extremely fine-grained, uniform, crystalline,
magnesian variety, usually drab or yellowish. As its surface can be
etched with weak acid, it may be employed for lithographic printing.
"Oolitic" limestone, so-called because of its resemblance to fish roe, is
composed of small rounded grains of lime carbonate of concentrically
laminated structure. When the grains approach the size of a pea the
rock is called "pisolite."

Limestone is composed primarily of shells of ancient sea animals.
Usually they have been comminuted so completely that no trace of
organic structure remains. Some beds, however, have been formed under
conditions that have left the shells almost intact or at least in fragments
well preserved enough to indicate their character and origin; these are
known as "fossiliferous" limestones. Some are made up almost entirely
of shells of one kind and are named accordingly. "Coral," "crinoid,"
and "coquina" are common types. "Chalk" is a fine-grained, white,
friable limestone composed largely of minute shells of foraminifera. In
places, oyster-shell beds are quite extensive in area and thickness and
are more or less firmly consolidated; therefore, they may be regarded as
shell limestones of very recent origin.

"Travertine" is a variety of limestone that is regarded as a product
of chemical precipitation from hot springs. As it is deposited in suc-
cessive layers and as chemical composition and conditions of deposition
may vary during this process, a banded structure commonly results. The
rock is characterized by the presence of numerous irregular cavities
ranging from the size of a pin's head or smaller to one-half inch or more
across. Some porous limestones are classed commercially as travertines,
though they differ from them in origin. Some travertines will take a
fair polish, but most of them are used with a sand-rubbed finish and
therefore are classed as limestones rather than marbles. Travertine
is used principally for interior walls, decorative effects, floor tile, and
steps. Some varieties are remarkably resistant to wear. Use as a
flooring material in the concourse of the Grand Central Station in New
York is a good illustration of the adaptability of travertine for service
where abrasion is constant and intense. Artificial travertines — syn-
thetic products — are sold as substitutes, but they have neither the wearing
nor the decorative qualities of true travertine, "Tufa" is a name applied
to a cellular calcareous deposit originating from mineral springs.

LIMESTONE 35

Another form of calcium carbonate is precipitated from cold-water
solutions in limestone caves and forms many ornate structures, such as
stalactites and stalagmites. It is incorrectly called "onyx," although
the more descriptive term "Mexican onyx" or "onyx marble" is often
applied to distinguish it from true onyx, a form of silica. As Mexican
onyx will take a polish and is highly ornamental it is classed with marble
rather than with limestone.

QUALITIES ON WHICH USE DEPENDS

Although innumerable deposits of limestone are to be found through-
out the country, only a small part of the rock will satisfy the exacting
requirements of dimension stone. Sound rock, free from deleterious"^
impurities and providing blocks of adequate size, is essential. Uni-
formity of texture, grain size, and color is usually required.

Purity is not regarded as an essential property of building limestone,
but chemical composition may have some bearing on quality. Silica
may make the stone more difficult to work. The appearance of sulphur
in an analysis usually indicates the presence of pyrite or marcasite,
minerals that may cause stains. Objectionable impurities are recognized
generally more easily by means of a microscope or a hand lens than by a
chemical analysis. Waste-stone by-products from relatively pure
deposits are more easily marketed than impure by-products.

Hardness and workability are important qualities. Limestones are
worked with comparative ease unless flint or other siliceous minerals are
present. Hardness has a direct bearing on the workability of limestone,
but its effect on use has minor importance, because limestones are used
where they are subjected to abrasion only to a limited extent.

Limestones are of many colors. Brown, buff, gray, or white varieties
are widely employed for building purposes, while the dark-gray or black
are in demand only for certain uses. Buff or yellow coloring is due to
minute grains of iron oxides — stable minerals that cause no stains. Sur-
face stains may result from oxidation of the iron sulphides or carbonates
sometimes present.

Sound structural limestone which is suitable in other respects is
usually strong enough for any use. Even for bridge piers, arches, and
tall monuments the strength of standard high-quality limestone far
exceeds the requirements of safety.

Pore space is variable; in most commercial limestone it ranges from
less than 0.5 to 5 per cent, though occasionally is much higher.

Appearance depends chiefly on color and texture. Blue limestones
may change to buff by oxidation of the iron. Generally, however,
permanence of color is preferred. Although uniform texture is usually
desired for the more ornamental stones, variations in both texture and

THE STONE INDUSTRIES

color are now much in demand for sawed and rock-faced stone used in
domestic construction.

USES

Limestone in the form of dimension stone is used principally in build-
ing. Its very limited application for monuments, curbing, and flagging
may almost be disregarded. The largest amount is employed in the form
of cut or rough-hewn blocks for exterior walls, either for entire structures
or for certain parts, such as window sills, caps, cornice, or base course.
Columns and balusters of the more ornamental types are widely utilized
for both interior and exterior building. Limestone is also employed
extensively for interior structural uses and decorative effects. Massive
blocks of cut limestone are used for bridges, dams, docks, sea walls, and
similar structures where strength, permanence, and resistance to shock
are essential.

Limestone for the construction of walls is of four main types — cut
or finished stone, ashlar, rough building stone, and rubble. The signifi-
cance of these terms is fully covered in a discussion of the general features
of dimension stone on pages 23 to 25. Limestone is being used increasingly
as ashlar, rough building stone, and rubble. The denser, harder varieties
are used for street curbing and to a smaller extent for flagging and
paving.

Production of dimension limestone by uses for a series of years is
shown in the following table:

Dimension Limestone Sold by Producers in the United States, 1925-1937,

BY Uses

Year

Building stone

Curbing, flagging,
and paving

Rubble

Total value

Cubic feet

Value

Cubic
feet

Value

Short
tons

Value

1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937

15,983,800

18,537,950

17,340,690

17,641,370

17,864,700

15,682,720

11,706,840

7,414,130

6,599,250

5,176,860

6,871,320

7,735,520

7,736,140

$16,092,079

20,391,597

18,820,045

20,193,963

20,649,257

18,535,293

10,858,697

7,028,224

6,416,223

3,391,455

2,700,747

4,662,716

5,096,535

129,730
167,780
223,370
322,560
471,880
346,040
166,260
122,000

78,610
116,610

93 , 700
178,000
167,950

$ 98,587

135,882

134,360

205,724

158,266

137,801

85,176

38,332

32,134

49,886

44 , 229

74,053

76,806

324,630
254,240
226,280
365,920
352,480
756,470
229,510
84 , 570
79,060
190,080
185,790
204,700
107,650

$513,387
476,545
400,790
705,723
693 , 678
623,100
296,426
84,308
94,046
179,791
276,569
181,415
136,028

$16,704,053

21,004,024

19,356,195

21,106,410

21,501,201

19,296,194

11,240,298

7,150,864

6,642,403

3,621,132

3,021,645

4,918,184

. 6,309,369

LIMESTONE 37

INDUSTRY BY STATES

Limestones occur in every State; but, except in widely scattered
localities in about one-half of the States, they are either unsuitable for
use, or conditions have been unfavorable for their development as sources
of dimension stone. The more important producing centers are briefly
described alphabetically by States in the following section. No attempt
is made to cover undeveloped deposits or to include all that are or have
been worked on a small scale.

Alabama. — The Bangor oolitic limestone of Palaeozoic age occurs in
Franklin County, northwestern Alabama. The deposit extends from
Newberg to Belgreen, about 20 miles, and has an average thickness of 20
to 25 feet, though it is much thicker in places. The best occurrences are
near Rockwood and Russellville. The rock is a characteristic oolitic
limestone similar to the extensive deposits near Bedford, Ind. Most of it
is of uniform texture, though some is distinctly veined. It grades in color
from light- and medium-gray to buff and is somewhat harder than
Indiana limestone. Many quarry openings have been made, and since
1924 production has increased notably. Recent developments are
chiefly near Rockwood, where a large stone-finishing mill is in operation.
Here quarrying is conducted with the most modern equipment, and the mill
is provided with all conveniences for rapid and skillful fabrication. The
easy workability of the stone gives the product a wide market range;
large contracts have been filled, even for cities as far north as Montreal,
Canada. The technique of quarrying and manufacture is covered in a
later section of this chapter, for while most of the discussion on this sub-
ject applies to Indiana, much of it will apply equally to Alabama.

Colorado. — A sandy limestone of Cambrian age, occurring near
Manitou, El Paso County, is marketed under the trade name "Manitou
Green-Stone." The body color is reddish brown, on which is imposed an
attractive green mottling. Calcium and magnesium carbonates con-
stitute about half the rock, the remainder consisting chiefly of quartz,
with a minor percentage of iron oxide. The green color is attributed to
the presence of glauconite or a related mineral. Quarry conditions are
favorable, as the rock occurs in easily separable beds having a maximum
thickness of about 2 feet. Tests by the Colorado Geological Survey
indicate that it is strong and durable. Active development of this very
attractive building stone began in 1930. Colorado travertine is discussed
on page 44.

Florida. — The coquina or shell limestone of Florida is probably the
first building stone used in America. It consists of stratified shell
fragments cemented together with finely divided calcium carbonate
derived from abrasion and comminution of the shells, and it is soft enough
to be cut easily with a handsaw. Although too porous for exterior use in

38 THE STONE INDUSTRIES

northern climates it appears to be quite enduring in the Florida climate.
Experiments are being conducted in search of a practical method of
hardening the stone and reducing its porosity to make it suitable for use
in climates subject to severe frost action.

It occurs in a belt about 200 yards wide on Anastasia Island and
was first quarried about 1580 to supply blocks of stone for building at
St. Augustine the famous Fort San Marco (the present Fort Marion),
which required many years for its construction. Though soft and porous
the fort walls were remarkably resistant to gun fire. St. Augustine is
called "the coquina city," because so much of this material has been used
for buildings. There has been little recent production in this district, but
a similar coquina limestone is quarried near Volusia, Volusia County. At
Islamorada on Windly's Island, Monroe County, a considerable quantity
of limestone is quarried and sold as cut and sawed stone and as flagging.
The Tampa limestone, occurring at New Port Richey, Pinellas County, is
quarried to some extent for building purposes. In places it is porous, like
travertine, and is said to be very pure, containing about 98 per cent of
calcium carbonate.

A soft limestone deposit at Marianna, Jackson County, in northern
Florida is known locally as "chimney rock." Many years ago it was
quarried in a small way and sawed into slabs when first taken from the
ledge. The blocks or slabs became quite hard after seasoning and were
used for making chimneys, house supports, or entire houses.

Florida travertine is referred to on page 44.

Illinois. — At times building limestone is quarried near Quincy, Adams
County; at Alton, Madison County; and at Joliet, Will County. In the
last locality the rock occurs in flat-lying homogeneous beds 6 to 30 inches
thick. It is a fine-grained, light-drab stone which upon exposure becomes
buff by oxidation of the small iron content. Large blocks are obtainable.
Production in the State is small, and practically all of it is for rough
construction.

Indiana. — Indiana limestone, also called Bedford limestone, Bedford
oolitic limestone, and Indiana oolite, is one of the most widely known
building stones. Figures compiled from returns of individual companies
to the United States Bureau of Mines show that, exclusive of a small
amount of stone sold for rough construction, data for which are not
available, and also exclusive of rubble, Indiana in 1930 produced 12,702,-
980 cubic feet of dimension limestone valued at $16,186,172, or more than
81 per cent of the total quantity and 87 per cent of the total value for the
United States. Corresponding figures for 1931 were 7,874,470 cubic feet
valued at $8,595,612, and for 1937, 4,442,360 cubic feet valued at $3,529,-
420. More than twenty large companies operate thirty to forty quarries
and mills. About a dozen more operate only finishing mills. The value
of finished products from independent mills is not included in the total

LIMESTONE 39

value. Its easy workability, adaptability for carving, attractive appear-
ance, endurance, and abundant supply have given to Indiana limestone
nationwide popularity. Chief production is in the Bedford-Bloomington
district in Lawrence and Monroe Counties, but building limestone is also
quarried at St. Paul, Decatur County, and at Romona, Owen County.

Structural Features. — Bedford oolitic limestone, known geologically as
the Salem limestone, is of Subcarboniferous (lower Carboniferous) age.
It rests on the Harrodsburg limestone and is overlain by the Mitchell
limestone. All the formations are tilted gently a little south of west,
with a dip of 34 to 70 feet per mile. Thus, in following the formations
westward they are found at gradually increasing depths beneath the
surface. In the eastern part of the area quarries are on the hilltops ; in the
west part, in the valleys.

The Salem limestone occurs in a massive bed 25 to nearly 100 feet
thick. In Indiana it extends from near New Albany on the Ohio River
northward through Salem, Bedford, and Bloomington to a point north of
Greencastle, a distance of about 125 miles. Active quarrying is confined
chiefly to the central part of the belt, from Bedford at the south to a few
miles beyond Bloomington at the north.

The rock has little tendency to split along bedding planes. Its
freedom from cleavage is a great advantage in carving, as corners and
projections are not liable to split off. Cross-bedding occurs in places.
Joints generally appear in two systems, the major having a general east
and west direction, with minor joints north and south. As joints are
spaced 20 to 40 feet apart in most places large, sound blocks are easily
obtained.

The rock is remarkably free from ordinary bedding or lamination
planes; however, unusual types known as "suture joints," "crowfoot,"
"toe nails," or "stylolites" occur in many places. They appear on the
quarry face as dark-gray to black jagged lines in zones a fraction of an
inch to several inches wide. The dark material is mainly organic matter
or chlorite, and the peculiar zigzag form is attributed to differential
solution under pressure. Some of the thicker stylolites tend to weather
rapidly at the exposed face but are not generally detrimental to quality
or strength. "Crowfoot" rock, sold under the classification "Old
Gothic," is preferred for certain architectural effects.

Bedford stone is described as oolitic because of its resemblance to fish
roe. The small, spherical grains or oolites are regarded as having orig-
inated from chemical precipitation of calcium carbonate in sea water.
Usually small grains of sand or shell fragments form nuclei of the spherical
masses, and, if crystalline, the calcium carbonate deposited about them
may be radial or concentric. True oolites are not so numerous in Indiana
stone as one would expect from the name, as most of the grains are simply
shell fragments of foraminifera or other marine animals. What is known

40 THE STONE INDUSTRIES

as select stone is fine-grained (less than 3'^4 inch in diameter), though
medium-grained (3-^4 to 3^^ inch) and coarse-grained (more than 3=-^ inch)
are also popular.

A "rift," or direction of easy splitting, is present in most Indiana
quarries. In places it is horizontal but more generally is inclined north
or south at a low angle and probably is due to crossbedding.

Color. — Indiana limestone is divided into two general color classifica-
tions, buff and gray. The buff color is regarded as a result of slow
oxidation of the small iron content, because the gray to bluish-gray stone
is generally found below ground-water level and the buff above. It is a
curious fact, however, that uniform gradation from blue to buff is rarely
seen; the boundary is usually sharp and distinct. The buff stone appears
in various shades, which in general are divided into dark and light buff.
Variegated rock is a mixture of buff and gray in the same block, though
weathering processes gradually blend the colors until little or no differ-
ence is observable. Variegated stone is preferred for the contrasted
color effects desired in modern architecture.

Hardness and Workability. — When first quarried Indiana limestone is
comparatively soft and is easily worked but when thoroughly dried it is
somewhat harder. Consisting as it does of an aggregation of rounded
grains, it has certain working qualities that are among its most admirable
characteristics. It can be readily planed, turned, or carved into any
desired form and is therefore well adapted for any type of architectural
design. It can be tooled so rapidly that it has an advantage in cost of
manufacture over almost all other stones.

Durability. — The statement is sometimes made that, because it is
slowly soluble in water containing carbon dioxide gas, limestone is not to
be classed with the durable rocks. Loughlin^ has pointed out, however,
that carbon dioxide gas, even in a humid atmosphere, has no corrosive
effect on limestone and that when dissolved in water it exerts a solvent
action so slow that under ordinary weathering conditions it would require
450 years for this solution alone to corrode the surface two-fifths of an
inch. Limestone, therefore, may be regarded as durable enough for all
ordinary uses.

Generally the heavier stone is the more durable because it is more
firmly cemented and less porous than varieties that are comparatively
light in weight. Weight per cubic foot may therefore be regarded as an
index of its durabihty. The average specific gravity is 2.3, and the
average weight per cubic foot about 144 pounds.

Most standard building limestones are unaffected by frost after
they are properly seasoned, but unseasoned stone is subject to damage;

*Loughlin, G. F., Indiana Oolitic Limestone; Relation of Its Natural Features to
Its Commercial Grading. Contributions to Economic Geology, 1929, pt. 1, U. S.
Geol. Survey Bull. 811, 1929, p. 113.

LIMESTONE 41

therefore quarry blocks should be exposed, with access of air to all
surfaces, for 1 to 2 months before heavy frost. Quarrying is discontinued
during the winter because of the damage that would result from the
freezing of freshly quarried stone.

Grades of Stone. — Loughlin,^ working in cooperation with Indiana
producers, has devised the following classification :

Buff; AA, statuary; unusually fine, uniform grained. A, select; fine, uniform
grained. B, standard; prevailingly medium grained with rather distinct bedding.
C, rustic; prevailing coarse grained. Gray; D, E, EE, correspond to grades
A, B, and C of buff stone. Variegated (buff and gray in a single block): F,
variegated statuary, corresponding to AA; G, variegated, corresponding to B
and C. Special grades: Hard, "Indiana travertine," very coarse grained with
many large shell holes; "old Gothic," or stone of any color or grade, with or
without "crowfeet" or other features that would exclude it from regular grades;
"short length" stone equal in quahty to the regular grades but in blocks smaller
than those usually sent to stone mills.

A limited supply of rock classed as Indiana travertine is available.
Although fine-grained stone is desirable, too rigid insistence on this
grade would work a hardship on the industry, as it would cause excessive
waste of other grades that must be quarried at the same time, neces-
sitating a higher price and automatically limiting the market range.
The coarser grained stone is equally as good as the fine; consequently
the grading is not excessively rigid, and a moderate tolerance is allowed.

Extent of Supply. — The occurrences of Salem limestone are very
extensive, but quarrying is necessarily confined to a zone near the
outcrop as the removal of more than 40 to 60 feet of overburden would be
unprofitable. Even in this comparatively narrow zone the supply of
rock will be abundant for many years. Naturally the supply of buff
stone is more limited than that of blue-gray. Although certain local
areas may be nearly exhausted, new deposits are constantly being
uncovered.

Prospecting in Indiana. — As the quality of stone varies from point to
point, careful prospecting is necessary before development work can be
undertaken. The essential features, such as color, grain size, and extent
of beds, can be determined from drill cores. Because the beds are almost
flat lying and changes in texture and color are gradual, prospect holes
may be spaced 100 to 300 feet apart, although some operators prefer
closer spacing. A log of the thickness, color, and texture of the limestone
found in each drill hole is kept.

Kansas. — A light-cream limestone has been quarried quite exten-
sively near Silverdale, Cowley County and white limestone suitable for
cutstone trim near Manhattan, Riley County. Other production in the
State is chiefly for local rough construction.

^ Work cited, p. 114.

42 THE STONE INDUSTRIES

Kentucky. — The most widely known building stone of Kentucky
is the oolitic limestone of Warren County quarried near Bowling Green.
The rock is similar to Indiana limestone in color, texture, composition,
and durability. It occurs in sound beds 10 to 20 feet thick ; and, although
it is notably uniform in composition, care must be taken in selection to
avoid small pyrite lenses that may cause stains on exposure to the
weather. A peculiar feature is the presence of bituminous matter which
gives the freshly quarried stone a displeasing coloration, but which
evaporates rapidly upon exposure, leaving a clean cream-white to
light-gray surface. Quite a number of quarries have been worked at
various times, but only two companies have produced building stone
during recent years. Rough blocks are shipped to Bowling Green for
manufacture into finished products. The stone has been used in many
large buildings throughout the Middle Western and Southern States
and is employed to some extent for monuments.

Maryland. — Dolomite quarried near Mount Washington at the
northern edge of Baltimore is used at times for rough construction in and
near the city. A deposit of attractive gray limestone near Texas,
Baltimore County, is also quarried for building purposes.

Minnesota. — Dolomitic limestones ranging from nearly pure white
to yellow or buff, occur in flat-lying beds in southeastern Minnesota.
Certain beds, notably at Mankato, are blue when first quarried but
turn buff on exposure, probably from oxidation of the iron originally
present as carbonate.

The chief producing centers are Mankato, Blue Earth County;
Kasota, Le Sueur County; Mantorville, Dodge County; and Winona,
Winona County. The stone at Mankato and Kasota is strong, attrac-
tive, and obtainable in large blocks; it is well-adapted for construction of
heavy masonry and bridges. The chief commercial beds at Kasota are
recrystallized to such an extent that the material will take a polish and
is therefore sometimes classed as marble rather than limestone. Yellow
and pink Kasota stones are popular for interior decoration. A gray to
white attractive and durable building stone is obtained high on the
river bluffs near Winona. In some ledges the stone is porous and is
marketed as travertine.

Missouri. — Stone quarried at Carthage and Phoenix is classed as
marble and is described in the marble chapter.

New York. — Limestones for building, both dressed stone and rubble,
are quarried near Syracuse, Onondaga County. A small amount is
produced elsewhere, chiefly for local rough construction.

Pennsylvania. — There are many important deposits of limestone in
Pennsylvania, but they are used very little for building purposes. Beds
that should furnish the best building stone are situated in the south-
eastern part of the State where geological forces have folded and shattered

LIMESTONE 43

them excessively. Cambrian and Ordovician limestones of Northamp-
ton, Lehigh, and Berks Counties were used for foundations and house
building many years ago. The rock is available only in small blocks
but apparently is quite durable. The date 1821 appears in the gable
of a limestone house about 4 miles north of Easton, Pa., and the building
apparently is still in excellent condition. Limestones of Cumberland,
Franklin, and Montgomery Counties have been used locally for dwellings
and arched bridges. Local limestone was used in the construction in
1766 of the Harris Mansion, the oldest house in Harrisburg, and also
for the Paxtang Church just east of that place built in 1740. Pennsyl-
vania limestones evidently have an interesting history, but they are
used very little at present. Limestones now produced in Pennsylvania
are classed chiefly as rough construction stone, and the annual value of
the output is S25,000 to $100,000.

Texas. — Texas limestone quarrying has exhibited increasing activity
during recent years. At Cedar Park, Williamson County, a ledge about
30 feet thick provides a pale-buff to cream oolitic limestone of even
texture, well adapted for carving. Certain beds contain large fossils and
are porous, resembling travertine. Large shipments of building stone
are made from these quarries.

At Lueders, Jones County, a deposit of thin-bedded, light-gray and
variegated limestone covering a wide area has been quarried quite
extensively. Three beds — 8 inches, 1 foot 5 inches, and 1 foot 10 inches
thick, respectively — are separated by loose beds about 2 inches thick.
Therefore, no channeling machines are required, as the rock is easily
removed by drilling and wedging.

Near Del Rio, Kinney County, a 15- to 30-foot ledge in layers 2 to 4
feet thick has been quarried over an area of 5 or 6 acres. The stone is
harder and less uniform than that quarried at Cedar Park.

Utah. — A fine-grained, light-colored, oolitic limestone is quarried near
Ephraim, San Pete County, and used as building stone in Salt Lake City
and Provo. Some has been shipped to San Francisco.

Wisconsin. — Limestone of Niagara age is quarried at Wauwatosa,
Mihvaukee County. It is light gray, with variations to white and buff.
Two types are procured, a finely crystalline compact limestone and one of
coarse granular texture in heavy beds. The chief market is in Milwaukee,
where the stone has been used for bridges, ashlar, footings, sills, and rubble.

A thin-bedded, hard, gray dolomite, exceptionally strong and durable,
occurring near Lannon, Waukesha County, has been used quite exten-
sively for curbing and flagging ; some is employed also as building stone.

OCCURRENCES OF TRAVERTINE

Travertine has not been produced extensively in the United States,
although sales have been recorded from a few States during recent years.

44 THE STONE INDUSTRIES

Some porous limestones sold commercially under this classification are
not true travertines.

A quarry near Bridgeport, Mono County, Calif., which, many years
ago, furnished what was regarded as marble for buildings in San Francisco,
was again operated in 1929. The stone comes in a variety of colors;
some of it, ranging from clear white to pale yellow and gray, is said to be
of the same texture and quality as the best Roman travertine. It is also
obtainable in orange, pink, red, and brown.

A deposit that compares favorably with the famous Italian travertine
has been developed about 6 miles east of Salida, Colo., close to the
Denver & Rio Grande Western Railway. The deposit forms one side of a
hill rising 250 feet from the valley floor and is worked as a shelf quarry
conveniently situated for waste disposal and with automatic drainage.
The exposure is 1,300 feet long and 200 feet thick. Joints are spaced so
widely that blocks large enough for monolithic columns are obtainable.
The rock is said to have a compressive strength of 12,000 to 14,000 pounds
a square inch and on account of its porosity weighs only 135 pounds a
cubic foot. It is light buff, is very attractive, and is being used widely in
Denver and other cities for both interior and exterior building.

Two other travertine quarries have been opened recently in Colorado,
one near Salida, Chaffee County, and one near Canon City, Fremont
County. Up to 1931 production was confined to terrazzo.

In 1932 production of travertine was begun at Gardiner, Mont., near
the north entrance to Yellowstone National Park. As the material occurs
in a variety of ornamental colors and is adapted for polishing, possibly
it should be classed as onyx marble. Several carloads have been shipped
to St. Paul, Minn., for sawing and finishing. Travertine also occurs west
of Landusky, Phillips County, Mont.

A deposit of rock well-adapted for architectural use has been worked
near Bradenton, Fla. The stone exhibits the characteristic porous
texture of Italian travertine and resembles it in general appearance.
Production has been recorded since 1929, some of the material being
sold under the trade name "Floridene" stone.

A travertine quarry was operated for a brief period near Cuthbert,
southwestern Georgia. The rock is brown to golden and of porous
structure. Limited amounts were sold for interior building and waste
material was marketed as chips for terrazzo floors.

The output of certain porous beds in the limestone bluffs near
Winona, Minn., is sold as travertine, though most of the limestone in this
district is massive and compact. Similarly, exceptional beds resembling
travertine occur in the Indiana limestone deposits, but very little is
marketed. An attractive porous limestone is quarried near Cedar Park,
Tex.

LIMESTONE 45

QUARRY METHODS

Quarry Plan. — Most deposits of limestone used as dimension stone
are approximately flat lying and of limited thickness. Thus, the stone
available in any one opening may be removed within a short time and a
new ledge uncovered. The abandoned pits may therefore be utilized for
disposal of waste and overburden from succeeding benches.

In Indiana, where a greater part of the building limestone is produced,
most ledges are 120 to 140 feet in width to permit service by a derrick
boom ; sometimes blocks from the most remote parts of the ledge must be
dragged. At large quarries a series of derricks is set in line and a long
ledge worked down in a succession of floors until all the good stone is
removed. The line of derricks is then moved back 120 to 140 feet and
another ledge begun. Stripping and waste from the last operation are
thrown into the opening previously made; thus, a wide area may be
worked out in successive strips.

Stripping. — In the Indiana district red clay covers the limestone beds
to a depth of 1 to 20 feet or more. In some places it is stripped by power
shovels into worked-out pits. The hydraulic method is employed where
the surface contour favors washing the soil into abandoned pits or other
low-lying areas. Mud seams are usually present in the upper level, and
the hydraulic method is especially advantageous for washing clay from
such irregular surfaces. However, loose rock fragments mixed with the
clay may hamper removal by water, and some other process may be
better. Hydraulic stripping has been described in a previous chapter
(see pages 14 and 15).

A second phase of stripping involves the removal of overlying non-
commercial rock, which at many quarries occurs to a depth of 5 to 15
feet immediately beneath the clay covering. In some quarries near
Bedford 40 to 60 feet of such waste must be removed. The method of
removal is governed chiefly by the nature of its contact with the under-
lying beds. If it is separated from the good rock by a layer of clay,
shale, or an open bedding seam that serves as a cushion, it may be
drilled and blasted with light charges of black blasting powder without
danger of shattering the commercial rock. In some places, however, the
rock overburden is continuous with that of good quality, which under such
circumstances would be easily destroyed by the shock of an explosive.
In such cases it is necessary to channel the waste and remove it in blocks,
a stripping process almost as expensive as removal of good stone. A more
recent development is adaptation of a wire saw for making cuts beneath
the inferior rock, permitting explosives to be used without damage to the
underlying ledge.

Where mud seams extend through waste rock into marketable stone
the clay which accumulates during removal of the upper benches must be

THE STONE INDUSTRIES

removed as a floor-cleaning operation, which is not properly regarded as
stripping.

Channeling. — After all overburden is stripped from the rock surfaces
the next step is to make primary channeling-machine cuts for block separa-
tion. A channeling machine operates with a chopping action similar to
that of a reciprocating drill. It is mounted on a frame with four wheels
and travels back and forth on a track. The cutting tool comprises three
or five steel bars sharpened to a blunt chisel edge and solidly clamped

Fig. 4.-

-Steam channeling machines at work in an Indiana Hmestone quarry.
Indiayia Limcstojie Company.)

{Courtesy of

together. When three bars are used the cutting edge is in the form of the
letter A^; when five are used they are in the form of two such letters, or
with the second A^ reversed. On channelers of one type the cutting tools
are secured with wedges to an upper and lower clamp. The bars are
undamped and lowered after every 6 inches of channel cut, and at a
depth of 5 feet the 9-foot steel is changed for bars 14 feet long. On
another type — the duplex electric channeler — the bars are set in a cross-
head and changed every 2 feet. Steam channelers were once the only
kind used and are still employed to some extent. They cut faster than

LIMESTONE 47

other types but require more labor. A steam boiler is attached to the
machine which cuts a single channel. The blows of the channel head are
actuated by a piston in a cylinder, the action being similar to that of a
steam drill. Steel is changed about every 2 feet. Some are of the
duplex type, but both machines work in the same channel. Single
channeling machines are advantageous for cutting unusual widths.
Steam channelers are shown in figure 4.

The duplex electric channeler is now widely used. The chopping
action is accomplished with cranks driven by 25-h.p. motors and intensified
by heavy springs. The machine operates on a track of 7-foot 2-inch
gage and cuts a channel on each side. The cuts are 8 feet 4 inches to
8 feet 5% inches apart and may be 8 to 12 feet deep. The cutting edge
of the steel is IJs to 2% inches wide and cuts a channel about 2 or 23^:4
inches wdde. The steel is reduced one-eighth inch for each change.
Cuts may be 50 to 100 feet in length; for long cuts several machines
operate on the same track. Some large quarries keep 20 or more machines
in use.

When a pair of cuts is completed the tracks are moved and a second
pair made. On the completed floor they average 4 feet apart, but occa-
sionally are narrower or wider. In some regions channels are cut parallel
with the east-and-west mud seams, while in other places they are at right
angles to them. Cross channels are made only for wall cuts, for removal
of key blocks, or as "head cuts" to divide strips that are too long to be
turned down en masse.

Where mud seams are present the first cuts are made wdth some
difficulty. Tracks must be supported with posts and scaffolding. It is
difficult to keep a cut straight on an uneven surface, and channeling
becomes slow and tedious until it has passed the irregularities. The
addition of water is not feasible until a fairly continuous channel is
obtained; therefore, cuttings must be removed by hand. In the regular
process a stream of water carries away the cuttings as thin mud, and
cutting is much faster wet than dry. After the quarry floor is leveled it
is relatively simple to move and place tracks.

The rate of channeling is difficult to determine because some operators
measure it in terms of actual cutting time, while others estimate on the
basis of average accomplishment over a long period. The most reason-
able time basis is "channeling hours," that is, the time for which machine
operators are actually paid. Using such a basis for time, and regarding
1 square foot of channeling equivalent to 33^^ cubic feet of gross produc-
tion, the calculated daily rate is 200 to 300 square feet for each duplex
machine. Most operators will estimate a faster rate, but they fail to
allow fully for all interruptions. The cost of channeling is 8 to 12 cents a
square foot; in fact, it is the largest single item of quarry cost and may
exceed half the total cost.

THE STONE INDUSTRIES

Wire Sawing. — The high cost of channeling has led some operators to
attempt more economical methods. The unqualified success of the wire
saw in Pennsylvania slate quarries offers encouragement, for there a wire
saw will do the work of two or three channeling machines with much
lower first cost, as well as lower operating expense. The wire makes a
cut only about one-fourth inch wide and thus wastes little rock as cuttings.
No tracks are required, the saw may be operated by one man, and the
power charge is small. It is particularly advantageous in cutting upper

Fig. 5.

-Method of cutting and removing key blocks in a limestone quarry.
Indiana Limestone Company.)

{Courtesy of

irregular beds. Its design and operation are described in detail in a
subsequent chapter on slate (see pages 255-260).

Two Indiana companies were using this equipment with fair success
in 1931. In one quarry a cutting rate of 26 square feet an hour was
attained under rather unfavorable conditions. Another company made
quite exhaustive tests in 1931. A cutting rate of 87 square feet an hour
was attained, and the average cost during the second month of operation
was 11.2 cents a square foot. Details have been published by Newsom,^
who directed the work.

Removal of Key Block. — In opening up a new floor where no free
face is present the most difficult task is removal of the first or key block.

» Newsom, J. B., Results of Wire-saw Tests. Trans. Am. Inst. Min. and Met.
Eng., vol. 102, 1932, pp. 117-121.

LIMESTONE

The block is channeled on four sides, and wedges are driven in the cuts
to break it free at the floor. In some quarries, after an 8- by 8-foot
block has been channeled the tracks are shifted, and two 2-foot blocks
are channeled as shown in figure 5. The narrower masses, known as
"pulling blocks," usually are comparatively easy to break loose by
wedging in the channel cut. When the block is free, corners are chipped
from the edges of the cuts to make room for the dogs or hooks, and the

a 1

Fig. 6.

-Arrangement of channel cuts for removing key blocks.

blocks.

a, 2-foot channel; 6, key

block is hoisted out, as shown in the figure. If only part of the block
is thus removed the process must be repeated with the lower sections.
If unusual delay and difficulty are experienced in removing the first
block, it may be advisable to break it up and remove it as waste. When
it is out of the way floor space is provided for removing succeeding blocks.
They are wedged free at the floor and removed one by one, providing a

^---.

A B

Fig. 7. — Diagram showing effect of rift on floor breaks, a, dip of rift; 6, wedge holes.
A, break in a direction up the dip of rift giving uneven floor; B, break in a direction down
the dip of rift giving a more uniform floor.

wider working space. Another method of removing key blocks is
shown in figure 6. The pulling blocks are in the center, as indicated.
A mass 2 feet wide is removed along the wall to provide space for slush
from the channelers. A third long cut is made 20 feet from the 2-foot
space, and crosscuts 4 feet apart are subsequently channeled. When the
pulling blocks are removed the 4- by 20-foot masses are turned down as

THE STONE INDUSTRIES

usual. Various modifications of the method are in use in different
quarries.

Bed Lifting. — After masses of rock 4 feet wide, 8 or 10 feet deep, and
50 or 60 feet long are channeled, the next step is to separate them at the
floor line by drilling and wedging. An air-driven hammer drill is used
to sink a series of holes 8 to 12 inches deep, 1 foot to 18 inches apart,
slanting a little downward from points near the floor line. They are not
made at right angles to the wall but at such an angle that wedges placed
in them may be sledged conveniently. They slant right or left, depend-
ing on whether the sledger is right- or left-handed. Plugs and feathers

Fig. 8.

-Method of turning down blocks in an Indiana limestone quarry.
Building Stone Association of Indiana, Inc.)

{Courtesy of

are placed in the holes and driven in succession until a floor break is
made. At intervals wedges are driven to full depth, and the pressure
being thus relieved most of them may be removed.

Commonly the rift of the rock is inclined at an angle of 5° to 10° from
horizontal, which may result in a very uneven floor. It is best to quarry
in such a way that floor breaks are made in the direction of dip of the
rift, which then tends to hold or guide the break to the bottom of the
channel cut, as shown in B, figure 7. If a break is made in the opposite
direction it will follow upward on the rift from the bottoms of the shallow
drill holes and reach a point several inches above the bottom of the
channel cut, as shown in A, figure 7. The floor will then consist of a
series of humps and hollows, and much waste rock will result.

LIMESTONE

More uniform breaks could probably be made by drilling some of
the holes almost the full width of a block and using long wedges in
them — a method in common use in marble quarrying — but apparently
such a plan has not been tried in limestone.

Turning Down Blocks. — After a block is wedged free it is turned down
in a horizontal position on the quarry floor before further subdivisions
are made. On a long block two notches or dog holes are made in the
back channel cut, wide enough to accommodate massive hooks. By
means of sheaves and tackle these are connected with another pair of
hooks firmly secured to the quarry floor some distance in front of the face.

Fig. 9.

-General view of a limestone quarry. (Courtesy of Building Stone Association of
Indiana, Inc.)

When a heavy strain is exerted on the cable by the derrick hoist the
block is gradually pulled over, as shown in figure 8. Bull wedges may
be sledged in the back channel cut to assist the process. Piles of broken-
rock "pillows" are so placed that the block falls on them and comes to
rest with little impact and without danger of breaking. Such "pillows"
are shown in figure 8. Figure 9 is a general view of a limestone quarry,
showing an unusually large mass of stone just turned down.

Subdivision of Blocks. — The next step is to divide the mass of stone
into commercial sizes. It is first laid out with a carpenter's square and
straightedge ; and if more than one grade of rock is present, a longitudinal
break is made between the grades. All subdivisions are made by plugs
and feathers or "slips and wedges," as they are called in Indiana. Holes

THE STONE INDUSTRIES

are drilled in line, 6 to 8 inches deep and 12 to 18 inches apart. Indiana
limestone may be drilled rapidly. One man with a hammer drill can
sink about four holes a minute. Plugs and feathers are then placed
therein. "Feathers" are strips of iron flat on one side for contact with
the wedge and curved on the other to fit the wall of the drill hole; two
are inserted in a drill hole, and a "plug" (a steel wedge about 6 inches
long) is driven between them. They are sledged lightly in succession,
beginning at one end of the line, to maintain an even strain on the rock.
Sledging is continued until a fracture appears. Common block sizes

Fig. 10. — Method of subdividing and hoisting limestone blocks. (Courtesy of Indiana

Limestone Company.)

are 10 by 4 by 3 feet and 10 by 4 by 4 feet. Where mud seams occur
or where separations must be made according to grades, many irregular
sizes may be produced. Figure 10 shows the method of subdividing
blocks.

Hoisting. — Steel or wooden derricks of about 30- to 50-ton capacity
are used for hoisting blocks from quarries. The derrick masts, of
swinging-boom type, are supported by 12 to 15 guy cables secured to dead
eyes in the rock or attached to buried timbers. Derricks now in use have
masts 80 to 110 feet high and booms 70 to 100 feet long. "Dog holes"
are cut on opposite sides of a block to hold the tips of grab hooks (dogs).
A chain passed through the eyes of the hooks draws them firmly against
the block, holding it securely, as shown in figures 5 and 10.

LIMESTONE 53

The end block is first raised about 3 feet at the outer end and lowered
again to the floor. This procedure crowds it outward, making a space
of a foot or more for attaching dogs. Dog holes are cut, hooks attached,
and blocks removed in succession and placed on cars or piled for later
disposal. Workers become very skillful in choosing positions for attach-
ing dogs so that blocks are balanced exactly. Each block is marked
with letters or numbers in black paint to indicate its classification and
for use in office records.

Cleaning Floor. — Waste-rock fragments, muddy cuttings from
channeling machines, and clay from seams extending downward from the
surface accumulate on the quarry floor and must be removed before a
succeeding floor is channeled. The cleaning of floors is usually slow,
costly, and somewhat disagreeable, especially in rainy weather. Waste
is shoveled by hand into great iron dump pans, which are hoisted out
and dumped into abandoned pits with the quarry derrick. If much
waste accumulates a power shovel may be used.

Transportation and Storage. — As the average quarry block weighs
10 to 12 tons standard railway cars are invariably used for haulage.
Large storage capacity is essential, for enough stone must be accumulated
to supply the demands of the four winter months when quarries are
idle. Outdoor storage or "stacking yards" may be maintained at quar-
ries, at mills, or at both places. A common method of storage is to pile
blocks within reach of derrick booms. They are usually piled high in a
limited area, and at times it is difficult to sort them. Overhead traveling-
crane storage is preferred by some operators, because the blocks are more
accessible and handled more quickly.

Scabbling. — Some companies quarry only, and sell rough blocks to
stone mills; others have both quarries and mills. Companies that own
no mills frequently ship blocks to distant points, and these must be
trimmed carefully to avoid freight charges on waste. The process of
trimming blocks to uniform rectangular shape is known as "scabbling."
It may be done at the quarry or storage pile and is, therefore, a sort of
transitional process that may be classed with either quarrying or milling.

Several methods of scabbling are employed. Scabbling picks
similar to ordinary miners' picks are commonly used to remove all
irregularities. One point is bent at a sharp angle toward the handle
for use in chopping dog holes for attaching grab hooks. Hand picks and
spalling hammers also are employed to remove corner masses from
blocks to be turned into columns. For squaring up ends of blocks some
companies use two heavy disks of iron about 3 feet in diameter which
run in opposite directions but in the same plane and with their peripheral
edges nearly meeting. On the face of each disk are attached two single
and one pair of cutting tools. As a block travels on a car the rotating
disks cut down the surface. Blocks scabbled with this machine are

54 THE STONE INDUSTRIES

easily recognizable by the two sets of semicircular grooves or markings
on their surfaces.

Scabbling saws are preferred by many, not only because they leave
a smooth, even surface, but also because in a single operation they remove
large projections which must be removed piecemeal by the pick or disk
method. Scabbling saws are of various types. Diamond-toothed drag
saws are used singly or in parallel pairs adjustable for width. Diamond-
toothed circular saws (commonly of 60- or 72-inch diameter) cut rapidly,
and if mounted in pairs adjustable in spacing may scabble both sides of a
block at once. The greatest limitation of the circular saw is the depth
of cut, as it can reach only from the arbor to the rim; a 60-inch saw can
cut only 26 or 27 inches deep and a 72-inch saw, 32 or 33 inches. This
difficulty is overcome by making one pair of cuts to the maximum depth
the saws will reach and then turning the block over and cutting from the
reverse side. If the cuts fail to meet the intervening rock is easily
broken.

A clever adaptation of a Carborundum scabbling saw has been
observed. The saw is mounted at the end of a shaft and secured with
counter-sunk set screws flush with the outer surface. When a cut is
made as deep as the arbor will permit the scabbled slab is broken off
with a hammer; and a second cut of equal depth may be made, for the
smooth outer surface of the blade interferes in no way with the sawed
surface of the block.

Scabbling planers are effective substitutes for saws. Rough blocks
are placed on a bed which travels between two sets of massive blades set
at right angles to the block and with edges vertical. Irregularities are
thus scraped from the surfaces of the stone. By screw-feed adjustment
the cutters are set closer after each motion, until a smooth surface is
obtained. On blocks 6 feet high each cut removes i^ inch of stone and
on blocks 4 feet high, 3^^ inch. About three blocks may be scabbled an
hour. A wire saw consisting of a ^{q- or H-inch three-strand cable
running as an endless belt driven by an electric motor is also used for
scabbling. Where the wire comes in contact with the stone it is fed with
sand and water. Several blocks may be lined up and cut at the same
time. The equipment may be operated by one man, and an average
cutting rate is 20 to 25 square feet an hour.

Various sawing methods are emploj^ed for slabbing off the sides of
blocks; but the ends are usually scabbled with picks, although they are
sometimes cut with wire saws or circular disk scabblers. The state-
ment has been made that rough, scabbled blocks weigh abolit 200 pounds
a cubic foot sale measurement, whereas smooth blocks weigh only 180
pounds a cubic foot, which indicates the advantage of scabbling by saw
or planer. Scabbling is done most carefully where blocks are prepared
for export trade or for shipment to mills long distances from the quarries.

LIMESTONE 55

MILLING METHODS

Mill Processes. — Quarried blocks are taken to mills for fabrication
into finished products ready for use in various types of construction.
Briefly, the steps in mill operation are drafting and pattern making,
block transportation, sawing, planing (including curved and molded
work), jointing, milling, turning, fluting, cutting, carving, packing, and
shipping. These processes are considered in some detail in the following
paragraphs.

Drafting and Pattern Making. — Before any cut-stone job can be
begun accurate detailed drawings must be made of every piece of stone
that differs from another in size or shape. Architects' drawings are
usually insufficient, for the stone must be fitted accurately to the steel
framework, and detailed data of the size and position of each steel
member are necessary before stoneworkers' shop drawings can be made.
These consist of elevations showing the position and dimensions of each
piece of stone. Some sizes and shapes may be duplicated many times in a
building; others may not be duplicated at all. Patterns for molded and
carved work are of zinc or other soft metal ; sometimes paper patterns or
stencils are used. For the most intricate carved work plaster models
are supplied by the stone mill or by the architect.

Few people realize how much labor and expense are involved in the
drafting required for a large stone structure. This so-called "paper
work "may cost one-half to two-thirds as much as the entire quarry
expense of supplying the rough blocks of stone.

Ticket System. — After shop drawings are made draftsmen prepare a
card or ticket for every block of stone. On each ticket is a drawing of the
block with exact dimensions indicated. A number is assigned, and if a
pattern is to be used the pattern number is given. Even though many
blocks of one kind are to be made a ticket is prepared for each. The man
in charge of gang-sawing first gets the ticket and cuts the block required.
As this piece of stone passes to the planer, jointer, and all subsequent
machines and operations, the ticket goes with it, and each workman
consults it before any work is begun. By this means workmanship is
constantly verified, and very few mistakes occur. The highest degree
of care and skill is required, for one small error in measurement or one
wrong blow with a tool may ruin a block on which much labor has been
expended. The above system is used particularly in Indiana. In some
New York mills one ticket or schedule is used for all blocks of a general
shape.

Handling Blocks. — Overhead traveling cranes with at least 70-foot
spans and lifting capacities up to 50 tons are used almost universally.
Mills are of two general types. Some are wide and equipped with two
pairs of crane tracks, one for a heavy crane used in handling quarry

56 THE STONE INDUSTRIES

blocks and placing them on the saw beds, while the second pair is
furnished with lighter, more rapidly moving cranes for conveying
smaller blocks as they pass from one operation to another. Some
means of transferring stone from heavy to light cranes is required. Other
mills are long and narrow, with one pair of tracks on which several
cranes operate. For example, there may be a 25-ton-, a 15-ton-, and a
71^^-ton-capacity crane on the same tracks. Some are of the three-motor
type, one of which is used for propelling the entire crane from one end of
the mill to the other, one for lateral motion to cover any point from side
to side, and one for hoisting. Most of them are of the two-motor type,
one motor with two friction clutches serving for both lateral motion and
hoist. In a very short time a block may be picked up at any point in a
mill and placed at any other.

Railway tracks enter the mills across the end, down one side, or across
the middle. They bring quarry blocks to the mills and carry away
finished products. All rough blocks and single unfinished slabs are
handled with grab hooks; finished and semifinished blocks or piles of
slabs, with cable slings or with slings of rubber belting to avoid damage to
corners and edges. Operators travel back and forth in cabs attached
to the crane. Some cabs are attached to one end of the crane, the
operator always being near one wall ; others are attached to the buggy
that moves back and forth from one side of the mill to the other. The
latter type has the advantage of placing the crane man always immediately
above the blocks handled, so that he can guide the movement accurately
and quickly. A ground force usually consists of two men, known as
"hookers," who attach and release hoisted blocks and signal the crane
man. This work requires much rapid walking back and forth in the mill,
for cranes travel at high speed, and after hooks or slings are attached,
hookers must as quickly as possible reach the point where the block is to
be placed.

Sawing. — The first step in manufacture is to saw rough blocks,
into either slabs or blocks, of the required dimensions. Gang saws
are almost universally used for this purpose. They consist of a series
of soft steel blades set in parallel position in a frame which has a
backward and forward motion. These blades may be spaced as desired
for thin slabs or thick blocks. Gangs vary in dimensions, one of average
size being 14 feet long, 8 feet high, and 8 feet wide.

Abrasives are fed to the blades with water; those most commonly
used are clean silica sand, most of which is obtained from Ottawa, 111.,
and "chats," a name given to a cherty rock obtained as gangue at the
Missouri lead and zinc mines and crushed to the consistency of sand.
Steel shot is also employed, chiefly to obtain the deeply scored, "ripple-
mark" surface desired for some architectural effects. When this type of
abrasive is used the blades are notched on the lower edge and used in a

LIMESTONE 57

straight-line drag-saw frame. Most gangs are of the swinging type and
are suspended from above by nearly vertical rods attached to the two
ends. As the frame moves back and forth, actuated by a crank and
connecting rod (pitman), the cutting blades lift toward the end
of each stroke. This permits sand to wash under them, and as they
start back on the return stroke the blade bears down on the sand which
abrades the stone rapidly. Some gangs have a straight backward-and-
forward motion, but the swinging type is more common. Sand or chats is
collected in a concrete trough beneath the gangs and pumped to a box
above the saws from which it is distributed, with fresh abrasives, to the
cutting blades. If much shot is employed it is shoveled for reuse rather
than pumped. An adjustable automatic gear feeds the gangs downward
at any desired rate. In the Indiana limestone district an average rate is
about 6 inches an hour.

A straight steel blade with diamond teeth on the lower edge is used as a
drag saw for making single cuts. A drag tooth is mounted with six
diamonds of about three-fourths carat size placed in alternate positions
on opposite sides of the cutting face. A single tooth may cost $40 or $50.
This saw will cut at a rate of 30 to 40 square feet an hour.

Circular diamond saws are used almost universally for making sub-
sequent cuts. Common sizes are 60 and 72 inches in diameter, though
smaller ones are sometimes employed. The blades are of steel one-fourth
inch thick, with a series of square notches around the rim. Steel teeth
mounted with diamonds are set in the notches and held in place with
copper rivets. A 60-inch saw, a size widely used, has 84 teeth and a
72-inch saw, 110 teeth. Teeth for rip saws designed for heavy service
are supplied with two 3^^- to ^s-carat diamonds. Jointing-saw teeth
contain 6 to 10 smaller diamonds, which give reasonably smooth stone
surfaces and cause less breakage of corners than ripsaws. Circular-saw
teeth cost $8 to $11 each. Extreme care and most exacting workmanship
are required in the manufacture of diamond circular saws to insure
accurate balance, uniform cutting, and true running. Each saw is
designed for a standard speed (11,000 to 13,000 surface feet a minute)
and should be run at no other. With care, a saw will perform constant
service for 6 months to a year without being conditioned. Resetting
costs about $1 a tooth if no diamonds are lost.

A ripsaw has a stationary mounting, and a bed actuated with a worm
gear carries the block of stone beneath it. An exception is the gantry
saw, which is mounted on a wheeled frame that travels on a track after
the manner of a gantry crane and spans the block resting on a timber bed.
A jointing saw is mounted on a movable frame actuated by worm gear,
which carries the saw through the stone.

The cutting edge of a diamond saw is cooled with a stream of water,
which also carries away the cuttings. An average sawing rate is 3 to 16

58 THE STONE INDUSTRIES

inches a minute, depending on the depth of the cut. Ripsaws cut faster
than jointers. The first cost of a diamond saw is high, but it cuts
rapidly, and with care maintenance cost is low.

Silicon carbide (Carborundum) circular saws are also in common
use. They are usually smaller than diamond saws and are of two
types — continuous rim, which are more generally employed, and toothed,
which are larger, approximately 30 inches or more across. They give
excellent service for the smaller cuts, as they leave smooth surfaces and
are less liable than diamond saws to chip the corners of stone blocks.

Some experiments are being performed in mounting saw teeth with
extremely hard alloys, such as tungsten carbide. Commercial develop-
ment has scarcely been attained, but the field offers wide possibilities.

Planing. — Planers are used for cutting stone blocks and slabs to
smooth surfaces and desired thickness and also for cutting moldings.
The frame that holds the cutting tool has lateral and vertical motion,
actuated by power-driven worm gear. The cutter is placed in position,
and a block of stone is carried beneath it on a traveling bed called a
"platen" at a rate of 30 to 45 feet a minute. A thin layer of stone is
thus scraped from the surface, and the process is repeated until proper
shapes or dimensions are obtained. Machines are equipped to cut tops
and sides of blocks simultaneously. For cutting moldings tools are
shaped in the blacksmith shop to fit exactly against patterns; that is, the
tool is the reverse of a pattern. If a great length of molding of one
profile is to be made, a Carborundum wheel, shaped in reverse form
or as a negative of the pattern, may be used, but in limestone the planer
is employed more commonly for this work. For both flat and molded
work the planer is a time saver, its estimated production being equivalent
to that of seven stone cutters using hammer, chisel, and modern pneu-
matic tools.

Planers are adaptable for curved as well as straight work. A second
bed or platen, capable of rotating through an arc of a circle, rests on the
regular bed. On some planers an arm pivoted on a fixed point at one
side is connected with the upper bed, and its length governs the curvature
of the arc. Another type is guided by a pin following any one of a
series of curved grooves having different radii. If a radius approaching
12 or 14 feet is required, it is accomplished through movement of the outer
end of the bar in a slot set at an angle. A stone block is placed on the
upper bed, and when the planer is operated in the usual way the tool
cuts a curved form, the shape of which is governed by the motion of the
block and the pattern of the tool. Garden seats and arches for doors,
windows, or ceilings are made with such machines.

A Carborundum planer consists of two saws with a drum of smaller
diameter between them, all of silicon carbide. The saws trim the sides
of slabs while the drum smooths the upper surfaces. The planer bed

LIMESTONE 59

travels at a rate of only 20 to 30 inches a minute, but it finishes the job
in one cut and accomplishes much more in a given time than an ordinary
planer with which many successive cuts may be required.

Turning and Fluting. — Lathes are employed for turning columns,
balusters, and similar forms. Large columns are first scabbled to
cylindrical shape and then mounted in lathes, essentially the same as
those used for wood or metal turning. The column rotates against a tool
actuated by machine-driven worm gear traveling slowly back and
forth the full length of the stone. The tool post is moved forward or
backward by a hand or automatic screw feed, which may be adjusted for
any change in diameter required for tapered columns. Limestone
columns are turned to a smooth surface, but final rubbing is usually by
hand. Ordinary lathes will handle 15- to 30-foot columns, and some are
specially designed for massive 50- or 60-foot columns. Smaller sizes
are used for balusters.

Many columns are fluted, the fluting is done on a lathe. A column
is first turned to the desired outer dimensions. The width and length of
the flutes are then laid out on the surface with pencil. The column
remains stationary while the fluting tool attached to the tool post of the
lathe travels back and forth. This process is continued until the line
bounding the flutes is reached. If a column is tapered the flutes may be
cut to shallower depth on the smaller parts of the column, which auto-
matically makes them narrower. When a flute is completed the column
is rotated with a hand bar, and the process repeated in the new position.
After this machine work the ends of the flutes are finished with pneumatic
tools, and the column is rubbed by hand. Carborundum fluters are
also used. A Carborundum wheel cut as a negative of the pattern is
generally used for making balusters, particularly if many of one kind
are to be fabricated.

Milling. — Some confusion exists in application of the term "milling."
The word is used in a general way to cover all mill processes, such as
sawing, planing, cutting, or carving, and is also applied to a particular
type of equipment known as a mflling machine. This machine consists
essentially of a rotating head with right-and-left and vertical worm-gear
motions. A movable platen provides front-and-back motion. The
head carries tools of various sizes and shapes, by means of which stone
may be cut in irregular patterns. This machine is particularly advan-
tageous in preparing for the carvers blocks in which deep recesses must
be cut, for it removes the bulk of the stone much more rapidly than it
can be cut away with hand tools. A skilled milling-machine operator
can outline lettering and intricate patterns, thus reducing hand carvers'
work substantially.

Cutting and Carving. — Cutting is usually defined as straight-line
work and carving as curved work. Carving requires more skill than

60 THE STONE INDUSTRIES

any other limestone-cutting operation and is usually done by experienced
workers. Many years ago all carving was done with chisel and mallet,
and these tools are still necessities for certain operations. Modern
pneumatic tools, however, have revolutionized the art and greatly
increased the production per man. The great bulk of the work is now
done with them.

At first the use of compressed-air tools was vigorously opposed.
It was feared that the art of stone cutting would be destroyed, and that
health would be impaired through vibration of the tools. Such fears were
unfounded, for pneumatic tools enhance the skill and artistry of the
carvers and lighten labor to a marked degree. Many a stonecutter of
advanced age, who could not bear the strain of constant toil with chisel
and mallet, has found his labor so lightened by pneumatic tools as to
add several years of active work to an already long experience.

The stonecutter uses a great variety of tools, heavy ones for removing
larger fragments when blocking out a design and smaller ones for com-
pleting the work. Intricate carving may require tools almost as fine as
those of a dentist. Patterns insure accuracy and symmetry. A pattern
may be placed on the surface of the stone and marked around the border
or through perforations, or the design may be transferred by dusting
with burnt umber. Models of the most complicated figures are made in
plaster of paris, and reproducing them in stone is work of the highest skill.

Carving adds greatly to the expense of preparing stone. Architects
who design structures requiring much hand carving must expect a cost
per cubic foot much higher than that for buildings consisting of plain
blocks. Oolitic limestone, however, carves more easily and tends to
split on the bed less than most other limestones, bringing it within
a cost range which greatly widens the field of carved-stone architecture.
Many beautiful structures, churches, chapels, libraries, and other
public buildings bear witness to the adaptability of oolitic limestone for
carving.

Finishing. — Much limestone used in buildings has no other surface
finish than that given by machines with which it has been worked. Cer-
tain parts, however, such as columns, may require smoothly rubbed
surfaces. Usually final finish is done by hand, the stone being rubbed
down wet or dry with sandstone, sand and water, or bricks of artificial
abrasives. A small electric-driven disk faced with sandpaper may
finish flat surfaces. Steel scrapers are also used and wire brushes
employed to brush all cuttings from the surface.

Nature of Finished Surfaces. — Architects and builders demand
various types of surface finish, A tooled surface, which is covered with
fine grooves in parallel lines, is made with a pneumatic or planer tool
having fine teeth. A bush-hammered surface is rough and pitted, as the
hammer used has a face covered with small projections. A hand-picked

LIMESTONE

surface is indented with a sharp-pointed tool, A small-fluted surface has
small, parallel corrugations. A four-cut surface is made with a planer
tool that has four corrugations to the inch. A rubbed surface is smoothed
by hand rubbing with sand and water or some other abrasive. A shot-
sawed or ripple surface is deeply scored or grooved by using steel shot as
abrasive for the gang saws. Chat-sawed stone is rough but smoother
than the shot-sawed. The chats used as abrasive in sawing are of
three different grades of fineness to give smoother or rougher surfaces as
desired.

Preparation for Shipping. — Building stone is a product so heavy that
provision must be made for handling all blocks by machinery, in such a
way that corners or edges will not be broken. For smaller pieces a pair

Fig.

-Interior of a limestone finishing mill

Limestone Company.)

of converging holes is drilled in an edge or face that will be covered when
the block is in final position in a building. Lewis pins, with eyes at the
top, fit loosely in the holes. Through them a chain is passed, and as it
is drawn tight the pins bind so firmly that the block can be hoisted safely.
For large, heavy blocks Lewis key pins are commonly used. The holes
which are drilled for them are enlarged at the bottom. The two side
keys are wide at the base and held apart in the hole with a center key
inserted last. All three are secured with a bolt which passes through
holes in their upper ends and also holds a ring for hoisting. Much
handling is done with slings or chains, lumber being used to protect the
edges. All blocks are numbered and lettered, to show their positions
in the structure in which they are to be placed, and carefully packed for
shipment, usually in open-top gondola cars. Each block is surrounded
with excelsior and limestone dust and packed so solidly that no damage

62 THE STONE INDUSTRIES

can result during shipment. For the Department of Commerce Building
in Washington, D. C, one of the largest stone buildings in America,
nearly 70,000 blocks of Indiana limestone averaging 1,500 pounds in
weight were used; 1,100 railway cars were required to haul the finished
stone.

Figure 11 illustrates the interior of a modern limestone finishing mill.

LIMESTONE PRODUCTS

Some companies quarry and saw only, selling the stone in blocks
or slabs. Standard-size blocks are most salable and command the highest
price. Because of the presence of mud seams or other reasons odd-size
blocks, usually designated "chunks," are necessarily produced. The
quarry operator who has no mill suffers some disadvantage, for while
off -size blocks may with judicious management be utilized to advantage
they are not disposed of readily and command a low price.

A second and larger group of companies both quarries and manu-
factures stone into finished products. The mills are either at quarries
or in near-by towns, the latter usually being preferred because the labor
requirement is large, and living conditions are more favorable than in
most quarry regions. A third group of companies buys sawed or rough
stock and manufactures products, but does not operate quarries.

Therefore, rough blocks, slabs, and cut stone or other forms of
building stone are the products chiefly marketed. Cut stone includes all
types of finished blocks, columns, sills, moldings, balusters, and carved
stone. It is the chief, though not the only, product of many limestone
mills.

A rougher type of building stone, known as "sawed or broken ashlar,"
is not usually regarded as a cut-stone product. It is particularly adapted
for residential work, though it is also used in larger structures. It is
much less expensive than cut stone and thus brings homes, having the
permanence and dignity of stone, within the cost range of people of
moderate means. This type of ashlar is fabricated in sawed strips usually
3 or 4 inches thick and in different height units that will combine to give
even-range levels if desired. It is sold either in strips, cut on the job
to specified or standard lengths that will fit together and make even
corners with very little cutting, or sawed on four sides and broken to
give various lengths. Random sizes and mixed colors give very attrac-
tive effects. Rough ashlar is comparatively inexpensive, because it
requires no drafting or pattern-making, no machine work except sawing,
no cutting or carving, and no careful packing for shipment and because
it may be set by a stone mason or brick layer. Its use is advantageous
to the producer because it permits him to use many small sizes that
would otherwise be wasted. It is of benefit to the user because it makes

LIMESTONE 63

it possible to build innumerable homes of moderate cost, low upkeep
expense, high rental and sales value, and attractive, dignified appearance.

COST OF QUARRYING AND MANUFACTURE

Quarrying and milling costs are both variable because they depend
on conditions that may be quite diverse in different localities, for example,
depth of overburden, degree of hardness of the rock, type of equipment
used, working efficiency, skill of the workers, and size of operation. The
general range of quarry costs is 20 to 30 cents a cubic foot of block stone.
The chief item is channeling, which ranges in cost from 8 to 12 cents a
cubic foot of recovered stone.

Milling costs are extremely variable because some blocks have little
work expended on them, and others require much labor. Sawing is a
heavy item of expense, the subdivision of rough blocks into slabs by gang
saws costing 35 to 45 cents a cubic foot of finished product. Sawing in a
second direction (jointing) costs 12 to 15 cents more. Planing, milling,
and cutting costs must be added for most products. Carving is very
expensive because so much labor is required per cubic foot produced.
Gothic carving is one of the most difficult operations to estimate; it
may cost as much as $7.50 a square foot of surface carved. The handling
of material is an item that should not be disregarded. Paper work,
including drafting, shop drawings, tickets, and patterns, may cost 15 to
20 cents a cubic foot on average jobs and exceed $1 a cubic foot on elabo-
rate structures. For jobs requiring a moderate amount of carved work
the total cost is $1.50 to $2.50 a cubic foot. If much carving, column
cutting, or curved work is demanded it may be much higher.

WASTE IN QUARRYING AND MANUFACTURE

Rock of inferior quality, which is regarded as overburden rather than
waste, usually overlies the Salem beds and is removed before quarrying
is begun. Aside from this overlying material, waste in the commercial
oolitic beds is high, and efforts are being made to discover ways in which
it may be reduced. Some of the waste is due to rock imperfections and
some to rock lost in quarry processes. The problem of waste has been
discussed in some detail by Newsom.*

Coarse texture was once regarded as a serious imperfection, but
tests have shown that coarse-grained stone compares favorably in
durability and strength with that of finer texture, and modern demands
for variety rather than absolute uniformity in texture have led to its
wider use. Fine-grained rock always has been in demand and still
commands a premium.

Erosion cavities filled with clay cause much waste, particularly
in the upper beds. Many small, irregular blocks, necessarily produced,

' Newsom, J. B., Quarry Waste in the Indiana Limestone District. Am. Inst.
Min. and Met. Eng. Tech. Pub. 444, 1932, 10 pp.

64 THE STONE INDUSTRIES

are discarded because they can not be used advantageously. Incipient
seams or '^drys/' small cracks difficult to detect, must be carefully
avoided. Some quarries contain many of them, and others have very
few. They are excluded so carefully that they are rarely seen in blocks
used for building. Stone is sometimes rejected because it is variegated in
color, but present demands have led to a wider use of such material.
Further waste results from quarrying processes. It is estimated that
1 square foot of channeling is required for each 33^^ cubic feet of gross
production. Therefore, if each channel cut is 234 inches wide at the
top, 4 to 5 per cent of the rock is cut away. Uneven floor breaks may
cause the loss of a zone of rock 1 foot or more deep at the bottom of
each floor. Crooked cross fractures, strain breaks, cutting of dog holes,
and other factors incident to quarrying further increase the waste. It
is estimated that not more than 40 per cent of the rock stripped and
blocked out in a quarry is recovered in usable form. Much high-grade
commercial material is also wasted as it passes through the mill in the
manufacturing process. Outside slabs from gang saws and rough ends
from jointers reduce the volume of every block by several per cent. Saw
blades convert much rock into fine mud. Each diamond-saw cut and
each stroke of a planer takes its small toll of stone, while in making
curved and irregular designs more than half of the mass may be cut
away. It is estimated that mill waste amounts to between 10 and 20
per cent of the gross footage entering a mill. The smaller percentage
is in mills where material is utilized to best advantage as, for example,
where cubical blocks are sawed diagonally to make two triangular corner
blocks or two cornices wide at one end and narrow at the other.

UTILIZATION OF WASTE

Limestone of commercial grade in the State of Indiana generally
analyzes 97 to more than 99 per cent of total carbonates. Building lime-
stones in various other States are also of high purity. Pure limestones
are useful for many chemical purposes, and some operators have sought
to develop markets that will absorb part of their waste materials. Some
high-grade material is burned into lime, which is used widely, not only
for mortar and plaster, but in paper mills and steel furnaces and for water
purification. Finer sizes of waste are used as agricultural limestone, in
glass factories, for tennis-court surfacing, as chicken grit, or as filler.
Many thousand tons from 4- to 12-inch size are sold as flux for open-
hearth steel furnaces, for which a very low silica content is demanded.
Many carloads of stone ranging from 1- and 2-man sizes to stones weigh-
ing 30 tons are sold as riprap and breakwater stone. Slabs of attractive
colors are sold as stepping stones, flagging, and for garden walks. If the
stone is suitable it may be utilized as railway ballast and concrete aggre-
gate. Mill ends and other small sizes are converted into ashlar. While

LIMESTONE 65

waste limestone can be used for many purposes, the amount consumed is a
mere fraction of the thousands of car loads of quarry and mill waste now
discarded.

LIMESTONE MARKETING

Under normal marketing conditions two-thirds to three-fourths of all
building limestone is sold as rough blocks or sawed slabs to mills situated
in large cities, where it is fabricated chiefly for small or moderate-size
building contracts. The balance of the production is manufactured in
mills operated in the quarry districts. Much of their output is devoted
to large projects. These mills, supplied only with shop drawings, can
fabricate stonework for a structure hundreds of miles away and can
supply in exact dimensions and in finished form thousands of blocks,
each fitted accurately for its particular position in the wall. Although
furnishing stone for large buildings directly from quarrying centers is
perhaps the most spectacular phase of limestone marketing, the impor-
tance of mills situated in consuming centers must not be overlooked.
They perform a vital function, for they supply stone to innumerable
users, many of whom require quantities too small to be obtained directly
from the great quarrying and milling centers.

The smaller limestone quarries in various States sell much of their
production directly to builders and contractors for local use. Some,
however, undertake fairly large building contracts or supply limestone
to be used in conjunction with other varieties of stone in both near and
distant projects. Some of it is handled through local mills in many
cities.

Bibliography

Anderegg, F. O., and others. Indiana Limestone, Efflorescence and Staining.
Purdue Univ. Eng. Exp. Sta. Bull. 33, 1928, 84 pp.

Ashley, G. H. The Geology of the Lower Carboniferous Area of Southern Indiana,
Indiana Dept. Geol. and Nat. Resources Twenty-seventh Ann. Rept., 1903.
pp. 83-84.

Beede, J. W. Geology of the Bloomington Quadrangle (including section on Utili-
zation of Waste Stone, by G. C. Mance). Indiana Dept. Geol. and Nat. Re-
sources Twenty-ninth Ann. Rept., 1914, pp. 190-312.

Hopkins, T. C., and Siebenthal, C. E. The Bedford Oolitic Limestone of Indiana.
Indiana Dept. Geol. and Nat. Resources Twenty-first Ann. Rept., 1897, pp.
291-427.

Kessler, D. W., and Sligh, W. H. Physical Properties of the Principal Com-
mercial Limestones Used for Building Construction in the United States. U. S.
Bureau of Standards Tech. Paper 349, 1927, 94 pages.

LouGHLiN, G. F. Indiana Oolitic Limestone; Relation of Its Natural Features to
Its Commercial Grading. Contributions to Economic Geology, pt. 1, 1929,
U. S. Geol. Survey Bull. 811, 1930, pp. 111-202.

66 THE STONE INDUSTRIES

Newsom, J. B. A Geologic and Topographic Section across Southern Indiana.

Indiana Dept. Geol. and Nat. Resources Twenty-sixth Ann. Rept., 1903, p. 281.
Richardson, C. H. The Building Stones of Kentucky. Kentucky Geol. Survey,

1923, p. 355.
Stone, Ralph W. Building Stones of Pennsylvania. Pennsylvania Topog. and

Geol. Survey Bull. Ml 5, 1932, 316 pp.

CHAPTER VII

SANDSTONE

VARIETIES

The term "sandstone" is applied to rock composed of small mineral
grains, usually quartz, which are cemented together more or less firmly.
"Conglomerate" is a name given to rock consisting of pebbles of various
sizes which are cemented together; if the pebbles are large and well-
rounded the rock is sometimes called " puddingstone " ; if angular in shape
it is called "breccia." "Quartzite" is a variety in which the individual
grains are cemented together with quartz so firmly that the rock fractures
as easily through the grains as through the cement. Some quartzites
look like massive quartz with scarcely a trace of their original fragmental
character. A "ferruginous" sandstone is one rich in iron and a "micace-
ous" sandstone, one in which mica flakes are prominent. "Arkose" is a
feldspathic or granitic sandstone composed of angular grains which have
resulted from the disintegration of granites, the debris thus formed
having been recemented into solid rock without any extensive water
action or decomposition. The siliceous sandstones may originate from
similar granite rocks, but they have been so thoroughly decomposed and
worked over by water before cementation that practically nothing is
left of the original rock except the rounded grains of quartz. A
"calcareous" sandstone is one containing a considerable amount of
calcium carbonate, and an "argillaceous" sandstone one containing an
appreciable amount of clay.

Sandstones are also named from their characteristic colors, such as
"bluestone," "redstone," or "brownstone." The term "bluestone,"
however, is applied to certain thin-bedded or easily cleavable sandstones
irrespective of color. The name "flagstone" is applied to sandstones
that split readily into thin slabs or sheets suitable for flagging. "Free-
stone" is a sandstone that can be cut or carved readily with equal ease in
all directions. "Canister" is a type of quartzite suitable for the manu-
facture of silica brick.

COMPOSITION

Sandstones consist essentially of quartz; some are nearly pure quartz.
Those consisting principally of other materials are rarely found, although
many contain minor quantities of feldspar, garnet, magnetite, and mica.
Muscovite or white mica is a common constituent. Iron oxides, calcium
or magnesium carbonates, and clay are other common accessory minerals.

68 THE STONE INDUSTRIES

SIZE AND SHAPE OF GRAINS

The grains of which sandstone is composed vary greatly in size.
Some sandstones are so fine-grained that they may be used for razor
hones. A screen test of a typical sandstone from the famous Amherst
(Ohio) district indicates that practically all the grains will pass through a
sieve having 40 meshes to the linear inch, and that one-third of the grains
are finer than 100-mesh. Sometimes the coarser, angular-grained sand-
stones are called "sandstone grits"; however, the use of this term is
often confusing because it is applied commercially to sandstones
which are well-adapted for abrasive purposes and not necessarily to
those of coarse grain; for example, the "Berea grit" of northern Ohio is in
places very fine-grained. Grains of sandstone may be well-rounded or
angular, depending upon the degree to which they were waterworn before
consolidation.

As pointed out in the section on the origin of sandstone, water has the
ability to sort and classify loose materials according to size. Some
deposits show remarkable uniformity in size of grains, a very desirable
feature. Usually the sizes of grains are nearly uniform throughout the
rock of one bed, and much greater variation is found in passing from one
bed to another. This is to be expected because sand of an individual
bed has been deposited under nearly uniform conditions over a wide area,
whereas succeeding beds may have been deposited after long intervals
and under quite different conditions of depth or water movement.

CEMENTATION

The usefulness of a sandstone depends greatly upon the nature of the
cementing material between the grains and the degree of cementation.
Of the four common cementing materials — iron oxides, clay, calcite, and
quartz — the last is most desirable, as it provides the strongest and most
durable stones. All stages of cementation are found in nature, from
incoherent sandstones that may be crumbled between the fingers to
indurated quartzites. All types between these extremes are used com-
mercially, but friable sandstones are useless as dimension stone. Some
sandstones are cemented more firmly in certain parts than in others.
Such lack of uniformity causes hard and soft spots, an undesirable condi-
tion for all ordinary uses.

As the cementing materials and degree of induration vary greatly
sandstones are the most variable of all common rocks in hardnQ^s, Con-
fusion may arise from this statement, for it may be supposed that as all
siliceous sandstones consist essentially of quartz, which has a hardness of
7, all sandstones will have the same hardness. However, this quality,
which is a measure of the ease with which stone may be scratched, is
governed by the degree of cementation, for scratching loosens individual

SANDSTONE 69

grains. Hardness, therefore, refers to the degree of adhesion between
grains rather than to the resistance offered to abrasion. In this sense,
therefore, it is synonymous with workability.

COLOR

. The purest sandstones are nearly white. Iron oxides are the more
important coloring agents. Limonite (2Fe203.3H20) usually gives
yellow, brown, or buff shades, and hematite (Fe203), darker brown or red.
Oxidation of iron-bearing minerals upon exposure may cause the rock to
change in color. If the change is uniform throughout, the general aspect
of the rock may not be impaired, but changes in streaks and spots may
detract greatly from the appearance.

Permanence of color is usually desirable. Generally the deeper
shades of red, brown, yellow, or buiT are permanent because they are due
to the presence of the stable iron oxides — limonite or hematite. Blue or
gray sandstones, which occur deep down in the lower ledges of a deposit,
may contain ferrous sulphides or carbonates which upon exposure will
oxidize to the more stable forms with gradual change to a buff or reddish
color.

Although it is generally claimed that uniform color is desirable, for
certain architectural effects diversity is now in demand. Blocks of stone
that would at one time have been thrown on the waste heap on account of
nonuniformity of color distribution are now being utilized for ornamental
building.

POROSITY

Sandstones are generally more porous than other rocks, although
quartzites may have as little pore space as granites. The percentage of
porosity of commercial sandstones ranges from 2 to 15. High porosity,
especially if the pores are small, is undesirable if the stone is exposed to
the weather in cold climates.

Pores or intergranular spaces in sandstone may be divided into two
classes — capillary and subcapillary. The former group includes openings
more than 0.00002 centimeter in diameter, and the latter, those of smaller
size. Water in pores of capillary size, termed "water of saturation,"
passes off readily when the rock is exposed to a dry atmosphere. Sub-
capillary pores contain "water of inhibition," which is released with
greater difficulty.

Normally the intergranular spaces of sandstone in an undisturbed
quarry ledge are completely filled with "quarry water," which, particu-
larly that part defined as "water of inhibition," carries mineral matter in
solution. When the water evaporates the dissolved material is deposited
as a cement between the grains, making the rock appreciably harder,
and subsequent wetting will not soften it. As evaporation takes place

70 THE STONE INDUSTRIES

at the surface, a sort of casehardening results. For this reason freshly
quarried sandstone works more easily than seasoned blocks. However,
some recent investigations indicate that the surface-hardening effect is
less pronounced than has been supposed.

The time required for the escape of quarry water depends on pore
size and rock structure. Rock with subcapillary pores requires a loijg
drying period, and one that parts easily along bedding planes usually
dries more quickly than one with no rift or direction of easy splitting.
If sandstone is exposed to frost action while the pores are filled with
water, the expansion caused by freezing may result in serious disintegra-
tion. Blocks should therefore be quarried in time to dry before a heavy
frost. Quarrying is usually suspended in cold climates during the late
fall and winter. Sometimes quarries are protected from damage in
winter by flooding them with water, scattering quarry refuse over the
floor, or covering the vertical face with cornstalks.

USES

Building Stone. — Sandstone is used principally for exterior and
interior building; that having siliceous cement is especially useful for
exterior work because of its insolubility. It may be sawed or cut as
even-course stone or as broken ashlar and used for entire walls or for
trim on buildings made chiefly of brick or other materials. It is also
employed for steps, sills, water tables, coping, pillars, or columns. For
interior use the more attractive types are demanded, particularly the
fine-grained stones adaptable for carving. Sandstone with low absorp-
tive properties is used in lavatories. That which splits readily into thin
slabs is used for floor tile.

Strong sandstones available in large blocks are used in bridge and
dam construction and in sea walls, retaining walls, and dock facings.
Irregular fragments having one good face are used as rubble. Sandstone
is commonly built into attractive masonry walls around cemeteries and
country or suburban estates.

Paving and Curbing. — Sandstone is used quite extensively for street
paving. Only those stones which consist of grains firmly attached to
each other with siliceous cement and which thus approach quartzite in
texture resist abrasion sufficiently to make good paving stones. Some
authorities claim that moderately cemented rock is better than quartzite
for paving because it presents a gritty surface and wears at about the
same rate as the cementing material in the cracks, thus maintaining a
level rather than a smooth, rounded surface. Sandstones that have a
good rift (easy bed splitting) and a good run (a second direction of easy
splitting, perpendicular to the bed) may be trimmed most readily and
therefore are most suitable for paving stones.

SANDSTONE 71

Curbstones may be made of material softer than that used for paving
stones. They are manufactured extensively in conjunction with paving
stones and at quarries where building stone and grindstones are made.
If the rock splits readily, curbing may be split out and hand-trimmed at
the quarry. The more massive sandstones are sawed into curbing.
Production is about five times as great in value as that of paving stones.

Flagging. — A type of sandstone known as ''bluestone" is well-
adapted for flagging or sidewalks because it splits readily into thin,
uniform slabs of large size. Sandstone is also sawed into thin slabs for
sidewalks, but concrete is used for this purpose so universally that
production of flagging is now a very small part of the industry.

Grindstones, Pulpstones, and Other Abrasives. — Only sandstones
having special properties may be used for grindstones. The grains
should be uniform, moderately fine, angular rather than rounded, and
cemented in such manner as to grind steel readily and at the same time
wear rapidly enough to prevent glazing of the surface. At several
quarries, especially in Ohio, grindstones are manufactured in various
sizes up to 7 feet 6 inches in diameter. Many similar stones are manu-
factured to grind pulpwood for making paper. Small pieces of very
fine-grained sandstone are used for making grindstones to sharpen
cutlery and scissors or for making hones, whetstones, and scythestones.

Buhrstone is a type of sandstone particularly adapted for the manu-
facture of millstones. Foreign buhrstone is a hard, tough, porous rock
consisting of silica mixed with calcareous material. American buhrstone
is a quartz conglomerate occurring on the eastern slope of the Appalachian
Mountains, notably in New York, Pennsylvania, and Virginia. The
New York variety, known as "esopus" stone, occurs in a strip about 10
miles long extending southward from High Falls in Ulster County. The
Pennsylvania variety, known as "cocalico" stone, occurs in Lancaster
County. In Virginia similar rock, known as "Brush Mountain" stone
is found near Blacksburg, Montgomery County. Miflstones were used
extensively for grinding equipment 50 years ago, but the industry has
declined greatly, par-tly because of the gradual disappearance of the old
master craftsmen skilled in dressing the stones and partly because of
the development of more efficient methods of grinding grain, paint, and
minerals.

The manufacture of sandstone into abrasive products is a declining
industry. Synthetic abrasives of the aluminum oxide or the silicon
carbide type made in electric furnaces are gradually displacing those
of natural rock origin. Segmental Carborundum pulpstones have lately
come into use.

Miscellaneous Uses. — Sawed slabs of fine-grained sandstone are used
widely for grave vaults. Dense, impervious rock is cut into thin slabs
for constructing laundry tubs and similar plumbing fixtures. Small

THE STONE INDUSTRIES

,-, ^ -^

ooooooooo

00(NiOCC05000000

lO t>. C^

<© •* ^

05 -H

t^ lO lO lO (M

C«5 IM ■* CO <N

l£l

■*

1—1

T-H

ooooooooo

(M^iO'^C^CClOOIOO
OOSCCt^-^fNcD^CC

CCCC^-*00OCC0500
-HOOI> CC(MiO(M— I

O -^ CC CC

CD
00

05
CC

• CC

1-H

OOOOCCOOOO
cDcDt^O-^IMlMt^lM

CD^OOiOOfNOit^-*

CCCCl>-O5CC^'*<C000
lOOOCC-^OSIMt^iOlM
05 CC CC CO ^ t^

CO
CD
CO

CO
CD

ooooooooo

t>-*005^cOCCI:^Tt<
CD-^OOOOlMCOC^t^OO

Ot^-*0(Nt^05»OCC
t^-<*<t>.-«*<05COlMiO'*
CO CC CD O --^ t»

^~' 03 j; 03

w o; g

S 5^

3 -^^

cr a;
a; <u

.3 O

a. 3
Ph

03 _o

3 3
3 o

a. 5

>
3 -'^ "3

<D O <U

.S "

O bC

3 o
3 43

O ^

SANDSTONE 73

amounts are fabricated into electrical switchboards and billiard-table
tops, and line furnaces and acid tanks. Cubical blocks may serve as
footings or underpinnings for posts under heavy structures. Sandstone
is employed for monuments to a very small extent. Highly indurated
quartzite is used for grinding pebbles and for tube and ball-mill linings.

PRODUCTION

The accompanying table, compiled from figures supplied to the
United States Bureau of Mines, shows production by principal uses of
sandstone employed as blocks or slabs.

INDUSTRY BY STATES

Sandstones suitable for commercial use occur in widely distributed
deposits in nearly every State. Those that have been worked for dimen-
sion stone on a fairly extensive scale during recent years are described
by States in alphabetical order.

Arkansas. — Novaculite, a highly siliceous sedimentary rock suitable
for abrasive purposes, is quarried at Hot Springs, Garland County.
The value of the stone depends upon its peculiar texture. It consists of
minute, interpenetrating, sharp-edged crystals with innumerable small
cavities between them — an ideal condition for maximum cutting power.
The rock is used chiefly for the manufacture of oilstones and whetstones.

California. — Sandstones of many varieties occur in more than 20
counties but during recent years production has been confined to only a
few quarries. A massive blue-gray and buff sandstone that has been
used for several notable buildings in San Francisco came from a deposit
extending for 8 miles in the northern part of Colusa County, but there
has been no recent production. A moderately fine-grained arkose
sandstone used more for breakwaters than for buildings is found west
of Chatsworth, Los Angeles County. A deposit of buff sandstone was
worked many years at Graystone, Santa Clara County, and provided
stone for buildings at Stanford University. Brown sandstone occurs
abundantly in Lespe Canyon, Ventura County. Stone for rough
construction is quarried in Santa Barbara County at times. A porous,
argillaceous sandstone merging into shale is quarried near Carmel,
Monterey County. An unusual feature is the presence in some of it of
a high precentage of opaline silica. It is used for building patios and
houses, as garden-wall rock, and for flagstones.

Colorado. — A sandstone that has been quite popular for building
purposes at times is quarried near Turkey Creek, Pueblo County.

Connecticut. — Sandstones of Triassic age occurring in the Con-
necticut River Valley formerly were worked extensively at Portland,
Middlesex County. The well-known "Portland brownstone" was
widely used as building stone in New York, Brooklyn, and other eastern

74 THE STONE INDUSTRIES

cities. The deposit is large, extending from New Haven to northern
Massachusetts, or about 110 miles, with an average width of 20 miles.
At Portland the stone is uniform, medium-grained, and reddish brown
and lies in solid, nearly horizontal beds. Though quite porous, most
Triassic stone is durable if carefully selected and properly used. Com-
plaint has often been made of the spalling of brownstone in buildings, but
deterioration has been due more to faulty construction than to defects
in the stone. Much of it was split into slabs and placed on edge, a posi-
tion which results in more extensive spalling than when blocks are placed
wdth the bedding horizontal. The stone is still quarried and gives excel-
lent service if properly placed in the wall.

Idaho. — Medium-grained light-buff and also fine-grained gray sand-
stones are quarried on Table Rock near Boise in Ada County. They
are used for local building in Boise and are shipped to Colorado, Oregon,
and Washington.

Indiana. — A sandstone quarry has been worked for several years in
northern Orange County, a few miles south of Mitchell. It is reported
that wire saws are used quite successfully in this deposit. Sandstone
for abrasive purposes is quarried at Floyds Knobs, Floyd County.
Orange County was at one time a source of considerable quantities of
whetstones. Building sandstone is quarried also at St. Meinrad, Spencer
County.

Kentucky. — In Kentucky the most important deposits are at Blue-
stone and Farmers, Rowan County, and Wildie, Rockcastle County.
The Rowan County stone is very fine-grained and takes an excellent
sand-rubbed finish. It is sold as sawed and cut stone for building pur-
poses, finer grades being used for mantels and other interior work.
Kentucky and near-by Ohio, especially Cincinnati, are the chief markets,
though some of the stone is shipped to distant cities. The Rockcastle
County stone was used chiefly for trimming, such as sills, caps, and
copings, but quarrying has been discontinued.

Massachusetts. — Triassic sandstone similar to the Portland (Conn.)
stone, ranging from red to brown, has been quarried extensively for
building purposes at East Longmeadow, Hampden County. Although
it is durable if used properly the stone has been in less demand during
recent years.

Michigan. — Grindstones are manufactured at Grind Stone City,
Huron County.

Minnesota. — The most important sandstone-quarrying region in
Minnesota is at Sandstone, Pine County. For many years the Kettle
River quarries at this place have produced an even-grained stone of
light-pink to yellow or brownish-red color. It is probably of Keweena-
wan age. Quartz is the cementing material, and the grains are cemented
so firmly that the rock approaches quartzite in texture. On this account

SANDSTONE 75

it is well-adapted for paving stones for which it is chiefly used. It has
also been employed quite extensively for interior and exterior building,
also as flagging and rubble and to a limited extent for furnace lining.

In southwestern Minnesota the Sioux quartzite of Huronian age is
prominently exposed in Rock, Pipestone, and Nicollet Counties, The
rock is extremely vitrified, having the appearance of massive quartz.
It is red and makes a very beautiful, durable building stone; however, on
account of its extreme hardness it is not used extensively. During
recent years material quarried at Jasper, Rock County, has been used
extensively to line tube mills and as grinding pebbles. For the latter use
it compares favorably in service with Danish flint pebbles.

Associated with the quartzite in Pipestone County is a bed of an
interesting red mineral called "catlinite" or "pipestone." This material
is described more fully on pages 343 and 344.

New Jersey. — Sandstone has been used extensively for bridge con-
struction in New Jersey. Recent production for various building pur-
poses has been confined chiefly to Raven Rock, Hunterdon County,
and Wilburtha, Mercer County. Argillite occurring in Mercer and
Huntingdon Counties has been used for construction of many buildings
in and about Princeton.

New York. — Several types of sandstone occur in New York, The
largest quarries are in the Medina formation, Orleans County. This
stone was formerly used to a considerable extent for building, but the
chief output now is for paving stones and curbing. Both red and gray
stones occur; the former is very attractive for building, and the latter is
best adapted for paving. Because the rock is very resistant to abrasion
it gives good service on streets having heavy traffic. Large quarries are,
or have been, worked at Albion, Holley, Hulberton, Medina, and other
places in Orleans County,

The sandstones most widely used in this State are the so-called
"bluestones" of Devonian age, which occur chiefly along the Hudson
River in Albany, Green, and Ulster Counties and along the Delaware
River in Sullivan, Delaware, and Broome Counties. Other outcrops
are in Wyoming County and in the counties bordering Pennsylvania
westward from Chemung. Typical bluestone is an argillaceous sand-
stone, which is usually dark blue-gray. It occurs mostly in thin beds
and splits readily into smooth, uniform, thin slabs. Thus, it is par-
ticularly useful for flagging, curbs, sills, caps, and steps. The annual
sales value of bluestone for the entire State is about three-quarters of a
million dollars.

Red Potsdam sandstones have been quarried in the northern Adiron-
dacks for building purposes, but none of the quarries are now in operation.
At times small quarries are operated in various parts of the State, mainly
for special jobs, but they are not regular and consistent producers.

THE STONE INDUSTRIES

Ohio. — Just as Indiana is the leading producer of block limestone so
Ohio leads in sandstone, producing between 50 and 60 per cent of the
total output for the United States. Extensive deposits of Mississippian
(lower Carboniferous) age appear in a broad belt which extends from
Portsmouth on the Ohio River in the southern part of the State almost
due north to Norwalk, Huron County, and from there eastward to the
northeastern corner of the State. Except near South Euclid the lower
member, the Bedford stratum, contains little sandstone of commercial
value. The largest quarries in Ohio are in the Berea formation, which

Fig. 12. — A large sandstone quarry near Amherst, Ohio. {Cov/rtesy of The Cleveland

Quarries Company.)

lies above the Bedford. The Cuyahoga formation, which lies above
the Berea and is separated from it by the Sunbury shales, is quarried
in Scioto County, southern Ohio. Pennsylvanian (upper Carboniferous)
sandstones outcrop throughout the eastern third of the State except in
the north, and are quarried in many places. The largest quarries, one
of which is shown in figure 12, are near Amherst, Lorain County,
where the rock lies in horizontal beds which were once the shore cliffs
of Lake Erie. The sandstones are fine- to medium-grained and are blue,
gray, buff, and variegated. Complete oxidation of impurities as a
result of high elevation has given a stable buff coloration to the upper
beds. The rock varies considerably in character from one bed to
another, and each bed may show adaptability for some particular use.
Thus, at different levels stone is obtained for building, for bridge con-

SANDSTONE

struction, for curbing, flagging, and rubble, or for grindstones. The
buff and variegated stones are used both for exterior building and for
interior work in office buildings, churches, and residences. Much of the
building stone is sold in rough or sawed blocks. Differences in texture
have given rise to various local terms. An evenly stratified stone that
splits well is called "split rock"; rock of irregular stratification, marked
by fine transverse and wavy lines, is called "spider web"; and massive

FiG. 13. — An attractive use of sandstone ashlar. {Courtesy of Briar Hill Stone Company.)

stone which shows no evidence of stratification is termed "liver rock."
The Amherst rock contains about 95 per cent silica; the remainder is
made up principally of lime, magnesia, iron oxides, and alumina. To
avoid injury to the stone through freezing of the quarry water, the
quarries are operated only about eight months in the year.

The quarries near Berea, Cuyahoga County, are about 40 feet deep.
The stone is a little darker than the principal products at Amherst and
is adapted chiefly for building, grindstones, curbing, and flagging.
"Euclid bluestone," quarried near Euclid in the same county, is finer-
grained than the Berea stone and must be selected carefully because

78 THE STONE INDUSTRIES

of the common occurrence of pyrite crystals. It is sawed for flagging,
steps, caps, sills, and laundry tubs.

Sandstones from near Empire, Jefferson County, and at Constitu-
tion and Marietta, Washington County, are used chiefly for grindstones
and pulpstones. A fine-grained sandstone from McDermott, not far
from Portsmouth, Scioto County, is quarried for a great variety of uses,
including interior and exterior building, burial vaults, grindstones,
flagging, and many small abrasive stones, such as hones and whetstones.

Sandstone quarried near Killbuck, Holmes County, is widely known
as "Briar Hill" stone and is popular for building purposes on account of
its variegated colors. The quarries are situated at a high level, and the
stone is brought down by cable cars. Production, chiefly of dressed
building stone, has increased greatly during recent years. Its use as
ashlar in home construction is shown in figure 13.

A quarry at Sherrodsville, Carroll County, produces sandstone which
is sold chiefly as sawed and dressed building stone. Sandstone for rough
construction is obtained at Lisbon, Columbiana County, and both
curbstones and rubble are manufactured at Youngstown, Mahoning
County. Other quarry locations are Sugar Grove and East Lancaster,
Fairfield County, and Kipton, Lorain County.

Ohio building sandstone is marketed throughout the Middle West
and even in eastern cities. Most of the other products are distributed
even more widely.

Pennsylvania.— Sandstones are widely distributed in Pennsylvania
and are of many different types. Carboniferous sandstones and quartz-
ites appear in many places. Triassic sandstone quarried at Waltonville,
Dauphin County, was sold in past years as a building stone under the
name " Hummelstown brownstone," but the quarries are now idle. Much
material has been quarried for bridge work and other heavy construction ;
Curwensville (Clearfield County), Koppel (Beaver County) and Ellwood
City (Lawrence County) are noteworthy centers of the most recent
production. Sandstone for rough construction is quarried at Avondale,
Chester County. A very attractive variety for interior and exterior
construction occurs at Waynesburg, Greene County, in the extreme
.southwestern part of the State. Many small quarries produce rubble,
rough building stone, curbing, flagging, and paving blocks. Devonian
bluestones similar to the occurrences in New York are quarried, prin-
cipally along the bluffs of the Delaware and Susquehanna Rivers in
northeastern Pennsylvania. Some of the more important production
centers are Pond Eddy and Kimble, Pike County; Alford and Stevens
Point, Susquehanna County; and Meshoppen, Wyoming County. A
stone ranging from a quartzite to a quartz-sericite schist is quarried near
Edge Hill, Montgomery County, for building stone and as a refractory
for furnace lining.

SANDSTONE 79

South Dakota. — Sandstone for building purposes has been produced
for many years near Hot Springs, Fall River County. The Sioux
quartzite is quarried as building stone near Sioux Falls, Minnehaha
County. The deposit is continuous with that quarried at Jasper, Minn.

Tennessee. — A thin-bedded quartzite occurs near Crab Orchard
and Crossville, Cumberland County. The rock splits into remarkably
uniform slabs ^s inch to 15 inches in thickness and is noteworthy for its
adaptability. The thin slabs may be used for roofing; thicker slabs for
floor tile, flagging, and steps; and the heavier beds, for building stone.
For many years it has been quarried in a small way, but the industry
expanded considerably in 1929 and 1930.

Virginia. — Sandstone of Triassic age was quarried many decades ago
at Aquia Creek, Stafford County. It supplied stone for the United
States Capitol, the White House, Patent Office, and other buildings in
Washington. The quarries were idle for many years but were reopened
and have provided a substantial supply of building stone for use in
Washington and other cities. The rock is light gray, streaked or clouded
with buff, yellow, or red, — combinations that are popular with architects.
Similar rock was quarried many years ago near Manassas, Prince William
County.

Washington. — Sandstone development in Washington has been
confined largely to regions having efficient means of transportation.
Pierce and Thurston Counties have the most available occurrences.
At Wilkeson, Pierce County, a medium-grained gray sandstone is
quarried for local use and for shipment to near-by States. It is sold as
cut stone, sawed stone, rubble, paving blocks, and pulpstones. Stone
which is dark gray at depth and dark or light buff above ground-water
level is quarried at Tenino, Thurston County, and used for building
purposes in Washington, Oregon, Idaho, and California. Abrasive stones
known as ''holystones" are at times manufactured from Tenino sandstone.

West Virginia. — Sandstones are abundant in West Virginia and
represent many geologic formations. A quarry in the Saltsburg sand-
stone at Kingwood, Preston County, has furnished good-quality building
stone for use in New York, Philadelphia, Washington, and other eastern
cities, but very little has been produced since 1914. Grindstones and
pulpstones are produced near Ravenswood, Jackson County, and near
Fairmont, Morgantown, Opekiska, and Uffington, Monongalia County.

Wisconsin. — A belt of Potsdam (Cambrian) sandstone, known as
"Lake Superior brownstone," skirting the southern shore of Lake
Superior has been quarried chiefly at Port Wing, Bayfield County, but
there has been little recent activity. The stone is a coarse-grained,
reddish-brown material that has been used in Wisconsin, in near-by
States, and to some extent in Canada. In the west-central part of the
State, chiefly in Dunn County, a southern belt of the Potsdam sandstone

80 THE STONE INDUSTRIES

also provides commercial stone. Fine-grained cream-colored and buff
stones, marketed under the trade name "Dunville Stone," are used for
exterior building purposes for entire structures or as trimming of schools,
churches, and other public buildings throughout the Middle West and
to some extent in the East. Rock for rough building stone, paving
blocks, curbing, and rubble is quarried in various other parts of the State.

QUARRY METHODS

Influence of Induration. — As previously stated, the workability of
sandstones probably varies more than that of all other common rocks,
owing mainly to the condition of cementation of constituent grains. The
degree of cohesiveness may range from loose and friable types to indurated
quartzites. Quarry methods are governed largely by workability. For
example, highly indurated sandstone can not be channeled but must be
blasted, with the probable result that much of it will be shattered and
wasted, whereas a soft rock may be cut into rectangular blocks with a
channeling machine, and the waste will be much less. Quarry costs per
cubic foot are usually much higher in the harder rocks.

Influence of Rock Structures. — Rock structures that have a pre-
dominating influence on quarry methods are joints, bedding seams, rift,
reeds, and run.

Joints. — Natural open seams or joints presumed to originate mainly
through compressional or torsional earth strains characterize most sand-
stone deposits. In flat-lying deposits they are usually perpendicular to
the bedding and hence are vertical, or nearly so. They generally occur
in two or more systems, the joints of which approximately parallel
each other. When occurring in two vertical systems at right angles
and spaced 10 to 40 feet apart, they greatly facilitate quarrying.

To promote economy, quarry walls are maintained parallel with the
major joint systems. Thus, joints may be utilized to take the place of
openings that must otherwise be made by channeling or blasting.
The term "cutter" is generally applied to closed or inconspicuous joints,
sometimes called "blind seams" or "closed seams." Usually they are
planes of weakness that must be avoided in dimension stone.

Bedding Seams. — Open seams parallel with the bedding occur com-
monly in sandstones and usually are of great advantage in quarrying.
If they are present at intervals of a few inches to 3 feet apart, the deposit
is described as "thin-bedded"; if at intervals of 10 or 15 feet, it is "thick-
bedded " ; rock in massive form with no open bed seams is " tight-bedded."
Deposits near Amherst, Ohio, are of the latter type.

Most sandstone quarries are situated in horizontally bedded deposits.
Such flat-lying beds afford the simplest type of quarrying. The Potsdam
sandstone of northern New York is an exception, as the beds dip 20 to 25
degrees, but very little quarrying is now carried on in this rock.

SANDSTONE 81

Rift. — Rift is the plane of easiest splitting in sandstone; almost with-
out exception it parallels the bedding. It is a variable property; some
beds split with the utmost ease, whereas others have so poor a rift that
the rock splits in other directions almost as easily as it does parallel with
the bed. Such rocks are said to be lacking in rift. Rift is due chiefly to
orientation of grains. The presence of flaky minerals like mica or clay
may increase the rift, for in the process of sandstone deposition such
grains tend to come to rest horizontally, parallel with the bedding. In
like manner, other mineral grains tend to have their long axes parallel
the bedding plane, and this parallelism increases to a marked degree
the ease of splitting.

Rift may vary greatly in successive beds of a deposit. In the Amherst
(Ohio) quarries the "split-rock" beds have excellent rift, which gives
smooth uniform surfaces. In "cross-grained" beds the rift is diflficult
and uncertain; it may slant at abrupt angles to the general bedding plane.
The "liver rock" has a massive structure with no indication of bedding
and consequently lacks rift.

In quarrying, a good rift assists greatly as it facilitates bed lifting
where open bed planes are absent. Ease of splitting and the smooth
surfaces obtained are also of great advantage in subsequent operations of
shaping blocks into various finished products in the mill or yard.

Reeds. — The rift may not be the same in all parts of the same bed;
that is, the rock may split much more easily along certain planes than
along others. This may be due to a change in sedimentation, such as the
deposition of a thin layer of foreign material, as clay, to which the sand
grains above and below do not adhere readily. Again, it may be due to a
pause in the process of deposition with a smoothing over of the surface
and a filling up of the irregularities that are essential to a condition
of relatively high cohesion perpendicular to the bedding plane. It may
also be due to parallelism of grain orientation in certain zones. Such
planes, along which the rock tends to split with greater ease than in inter-
mediate planes, are termed "reeds." They are characteristic of many
bluestone deposits. The quartzites near White Haven (Pa.) split easily
along reeds marked by fine white lines and with difficulty in intermediate
positions. Like rift, the reeds are very helpful in separation of blocks.

Run. — The term "run" is applied to a second direction of easy split-
ting less pronounced than rift. It is also called the "breaking way" or
"grain," though the term "grain" is used by some quarrymen as a
synonym for rift. Usually the direction of run is perpendicular to the
rift, and therefore in flat-lying beds the run is in some vertical plane,
since the rift is horizontal. Bownocker^" states that from Berea to Berlin
Heights, Ohio, the run is nearly east and west — that is, it parallels the

1" Bownocker, J. A., Building Stones of Ohio. Geol. Survey of Ohio, ser. 4, Bull.
18, 1915, p. 111.

82 THE STONE INDUSTRIES

old shore line. Run is probably due to orientation of minerals and in
the above locality prevailing ocean currents at the time of deposition
may have arranged the minerals with their long axes parallel to a particu-
lar direction of the compass. In some sandstone deposits a distinct run
is recognizable and is of considerable advantage in giving smooth,
straight, broken surfaces or in permitting wide spacing of drill holes
for blasting or wedging. In other deposits it is absent or is so indefinite
that it exerts no apparent influence on quarry processes.

Quarry Methods in the Softer Sandstones. — By far the larger part of
the sandstone produced in the United States is from the softer types of
moderately easy workability. Channeling machines may be employed
in such stone, the extent of their use depending mainly on joint
systems. Where few joints are found it may be necessary to channel
all wall cuts and whatever other cuts may be required for separating
the larger masses of rock, except where an occasional joint may be utilized.
The larger quarries in northern Ohio are of this type. If joints are in one
parallel series, spaced 20 to 50 feet apart, it may be necessary to channel
wall cuts only along the side at right angles to the joints. These are
called "back-wall cuts." Where joints are in two intersecting systems,
meeting approximately at right angles, channeling may be required only
for the removal of key blocks. In deposits where joints are more
closely spaced, channeling machines may not be required, the
necessary breaks being made by blasting or wedging. An effort is always
made to work into such deposits in the direction of convergence of the
joints in order that blocks may be removed without binding against
walls. Sandstone deposits near Springfield, Mass., and Hummelstown,
Pa., are of this type. Wire saws, described in a later chapter on slate,
are used to a limited extent as substitutes for channeling machines.

Quarry methods are influenced greatly by the nature of the bedding.
In massive, tight-bedded deposits floor breaks must be made by wedging,
and in heavy-bedded deposits like those at Berea, Ohio, large masses are
channeled and subsequent breaks made with black-powder shots. Cham
neling usually is required only for wall cuts in thin-bedded deposits, and
wedging generally is better than blasting for further subdivision because
straighter breaks may be made and less waste results. Deposits of this
kind occur near South Euclid, Ohio, and Farmer, Ky. A good rift
greatly assists quarrying and is especially advantageous in tight-bedded
deposits where floor breaks are required. If the rift is good, a mass of
stone 12 to 15 feet wide may be lifted by wedging, whereas, in a "liver
rock," beds are rarely lifted in widths of more than 5 or 6 feet.

Quarry Methods in Indurated Sandstones. — As a rule, sandstones
sufficiently indurated for good paving blocks are too hard to be channeled
economically, and blasting or wedging must be substituted. Quarrying
in such deposits is therefore more complex and costly than in the softer

SANDSTONE 83

types. Even in some hard rocks channeling machines are used for wall
cuts because much shattering results from blasting if only two free
vertical faces are present. In best practice, quarry walls are maintained
parallel with the major open joints, which are utilized wherever possible
instead of channel cuts. Larger masses are subdivided by separating
along bed planes and making cross breaks by wedging in drill holes in
directions of rift and run, if such are present. Easy splitting of beds and
conveniently spaced vertical open joints are favorable structural features.

QUARRY PROCESSES

Channeling. Rate of Cutting. — When sandstone was first quarried in
the United States channels were cut with hand picks wide enough to
admit the body of a workman. About 1880 this slow, wasteful method
was superseded by steam-driven channeling machines capable of making
cuts 6 inches wide or less. Channeling machines of the steam, electric,
and electric-air types similar to those described in the preceding chapter
on limestone are now widely used. The rate of cutting depends on the
condition of cementation of the rock and ranges from 100 to 500 square
feet a day. If hard, flinty masses are encountered the rate will be
diminished temporarily, and the channel cut may be diverted from its
straight course. Usually the average rate of cutting is much less than the
maximum rate of which the machine is capable, because heavy blows
struck by channel bars when a machine is driven at its maximum capacity
tend to shatter or "stun" the rock. "Stunning" is a quarryman's term
for the production of impact fractures that may extend a foot or
more into the rock and thus waste otherwise good stone.

In terminating a channel cut in solid rock the cutting out of the lower
corner to give a vertical end is slow and tedious, but sometimes is greatly
facilitated by sinking a 4-inch vertical drill hole at the place where the
cut is to end.

Wear on Steel. — Channeling in sandstone is quite different from that
in limestone or marble. Although the rate of cutting may be much
faster the steel wears much more rapidly on account of the abrasiveness
of the sand grains. In the quarries of northern Ohio the machine usually
works back and forth on a cut about 30 feet long, and for such a cut the
steel must be changed about every 18 inches of depth attained because
of the loss in gage from wear. The first set of bars makes a cut about
4 inches wide, and each successive set must be narrower than the preced-
ing to avoid binding. Until recently cutting was done dry as the steel
wears more rapidly if water is added. One or two men were employed
at each machine to scoop out the sand cuttings, which in soft sandstone
amounted to several tons a day. Wet methods are now used.

Maintaining Minimum Number of Channel Cuts. — Channeling is more
expensive than blasting or wedging per square foot of surface obtained

THE STONE INDUSTRIES

and therefore is employed only for wall cuts, for separation of key blocks,
and for whatever other cuts may be necessary to prepare a block or mass
of stone for wedging or blasting. The latter processes are very ineffective
or wasteful unless the mass to be separated has five free faces, leaving
only one to be broken free. Thus, the mass of stone shown in figure 14
had only four free faces before channel cut "x" was made, namely, the
two sides, front, and top, and therefore, it could not be wedged or blasted
effectively. After cut ''x" is made it is fast at the floor only and there-
fore has five free faces. A floor break, "a," may be easily made by
wedging, and the block may be subdivided further by wedging or blasting

at "b." For this and each sub-
sequent break there will always
be five free faces. Quarrying
should be so planned that the
least possible channeling may be
done to attain favorable wedging
or blasting conditions. Vertical
joints may be of great assistance
Fig. 14. — Separating blocks with five free in obtaining the necessary num-

faces. X, channel cut providing fifth free , £ r £ ta • i -u

face; a, first break; b, second break. bcr of free faces. It IS also ob-

vious that open bedding planes or
a good rift will reduce the number of channel cuts.

Direction and Spacing of Cuts. — Channel cuts should parallel or be
at right angles to the major jointing systems. The spacing of channel
cuts should be governed by the size of quarry block desired; that is, the
number of feet between cuts should be multiples of the final quarry-
block dimensions.

Drilling. Machinery. — Tripod drills, bar drills, and hammer drills
are the chief types used. The first is a reciprocating drill mounted on a
tripod, and the second is a similar drill attached to a horizontal bar
supported by four legs. The tripod must be moved to a new position
for each hole drilled, but a line of holes may be drilled from one position
of the bar, the drill being moved along and clamped successively in new
positions. Bar and tripod drills usually are operated by steam. A
hammer drill is a nonreciprocating impact drill with an automatic rotat-
ing device. It employs hollow-steel drill bits through which the exhaust
air passes and blows the cuttings from the hole. It is usually unmounted,
is held in position by a handle bar, and may be moved with very little
loss of time. This offers certain advantages, particularly in thin-
bedded rock where holes are shallow and frequent moves are
necessary.

Compressed air generally is preferred to steam for quarry drilling,
particularly in cold climates where the condensation loss of steam is
heavy. Moreover, when steam drills are used water must be supplied

SANDSTONE 85

to remove the cuttings, which necessitates extra labor and makes a wet
or muddy floor.

Drill Steel. — Drill steel should be of a consistency that will withstand
excessive abrasion. Efficiency in drilling depends largely on the shape
of the bit. As narrow wings wear away quickly the drill head is shaped
to keep as much steel as possible near the circumference of the bit.
Most sandstones cut rapidly, therefore drill bits must have grooves large
enough to provide easy clearance for cuttings. Some drillers prefer
square bushings to hexagonal, as they do not wear off so quickly.

Rate of Drilling. — The rate of drilling varies with the hardness of the
stone; 1 foot in 38 seconds for a l^:4-inch hole has been recorded in a
northern Ohio quarry. Holes of )^ inch diameter were drilled in White
Haven (Pa.) quartzite at a rate of 3 inches in 35 seconds, a much slower
rate for holes of very small diameter.

Circle-cutting Drill. — In some localities where grindstones or pulp-
stones are made, rectangular blocks are scabbled to a circular shape.
In southeastern Ohio it has been found more convenient and less wasteful
to cut out circular blocks in the quarry with a machine known as a
"ditcher" or "circle-cutting drill," which is supported by tripod legs and
a vertical bar which fits into a 4- by 4-inch square hole in the surface of the
rock. The drill is attached to one end of a heavy crossbar, with a
counterbalance weight at the other end, and is rotated by a worm gear.
By securing the drill in different positions on the bar the diameter of the
circle to be cut may be varied. In cutting a circle 7 feet in diameter the
steel is changed about every 6 inches in depth, and each successive drill
bit is about one-fourth inch smaller to allow for loss in gage by wear. A
four-pointed star-shaped drill head is used. If cuts run from their true
course, as, for example, at the point where they meet other cuts, a
sharp-pointed bar is used to trim and straighten them. It is claimed that
a ditcher will cut as many square feet in a day as a channeling machine,
and much less time is required to set it up, as no tracks are necessary.

When a circular cut is completed a drill hole for the floor break is
made by means of an air drill which slides on a horizontal bed. The
drill is held in proper position and advanced by means of a hinged handle
and crossbar.

Blasting. Explosives. — Black powder is used almost invariably for
blasting dimension sandstone because dynamite unless of very low grade,
gives a sudden and violent explosion, thus shattering the rock too
greatly. Just enough powder should be used to make the fracture, and
no more.

Knox System of Blasting. — The Knox system has two essential fea-
tures— a grooved drill hole and an air space above the charge. Holes
are drilled nearly to the bottom of beds and reamed or grooved with a
flanged tool driven into the hole by sledging or operated as a drill bit

THE STONE INDUSTRIES

with the rotating device of the drill thrown out of gear. The grooves,
about one-fourth inch in depth and on opposite sides of the drill hole, are
made exactly in line with the direction along which the break is to be
made. A small charge of black blasting powder is added, and a plug
of cotton waste or other suitable material is placed in the hole some
distance above the charge. The hole above the plug is filled with sand
or other stemming. When an air space is thus provided the force of an
explosion is exerted over a relatively wide surface and causes less shat-
tering of rock than when the intensity of the force is localized in one
spot. Moreover, the explosive force, as it enters the grooves formed by
the reamer, tends to give ^ straight break. In the heavy-bedded rock

Fig. 15. — Uneven sandstone surface resulting from a break oblique lo the "run.'

near Berea, Ohio, the system is modified by leaving air spaces above and
below the charge.

Methods of Shot Firing. — For single shots either a fuse or an electric
firing machine may be used. Where a number of drill holes are to be
fired at once electric firing is necessary and may be done with a hand-
operated machine or by connection with the quarry current.

Arrangement of Drill Holes. — Holes for bed-lifting are drilled in line
with the bedding planes or rift. If the rock has a pronounced "run,"
as described earlier, vertical breaks are, in best practice, made in line
with it. If breaks are made oblique to the run two disadvantages are
entailed. First, the rock splits with greater difficulty, and holes must
be closely spaced ; and second, a very uneven surface is obtained. Figures
15 and 16 illustrate the contrast in surfaces obtained in making breaks
obhque to the run and parallel with it.

SANDSTONE

blasting for Subdivision of Larger Blocks. — The preceding discussion
of channeling and blasting relates almost entirely to- separation of larger

Fig. 16. — Smooth sandstone surface resulting from a break parallel to the "run."

rock masses from solid ledges. These masses usually are subdivided by
blasting in heavy-bedded rock and by wedging in thin beds. It is a
generally recognized principle that the blast should be centered; that is,
an equal mass of rock should be on each side of the line of fracture. If
drill holes are so placed that the rock
mass is not balanced properly, the
break tends to run toward the lighter
mass. Therefore, the process of sepa-
ration is a halving of the masses suc-
cessively until blocks of the desired
dimensions are obtained.

The procedure in an Ohio quarry
illustrates a typical process of sub-
division. As shown in figure 17, the
primary masses are 44 by 26 feet.
Fractures made by blasting are shown
by small letters. The shots are dis-
charged in order of lettering, a, h, c,
d, e. The final subdivisions give a
series of blocks 63-^ by 5,i^ feet, a size
most convenient for curbing and flagging. This indicates the foresight
necessary in selecting for the larger masses dimensions suitable for eco-
nomical subdivision.

In rock with a pronounced run most subdivisions may be made by
blasts in single, centrally located, drill holes. If the break is inclined

<— -26-— -*

-«.

Key Blocks

Fig. 17. — Method of subdividing
blocks in an Ohio sandstone quarry.
Breaks are made in the order of lettering,
a, h, c, d, e.

88 THE STONE INDUSTRIES

to the run, or if the run is poor, more than one blast hole may be required.
Shots in single holes are commonly used for breaks up to 15 or 20 feet
long. If the mass to be separated is more than twice as long as it is
wide it is advisable to use at least two holes, which should be so arranged
that the center space is a little more than twice as long as the end spaces.
If the mass to be broken off is a small part of a much larger mass, the
break tends to curve at the ends and slant toward the lighter part. This
tendency may be overcome in some measure by blasting in two drill
holes with a relatively long center space between.

Wedging. Operations in Which Wedging Is Employed. — Bed-lifting
and subsequent separation of blocks on the bed or rift are accom-
plished almost exclusively by wedging. Vertical breaks are made by
wedging, except in heavy-bedded rock, where blasting usually is
employed.

Type of Wedge Employed. — For wedging in drill holes quarrymen use
the " plug-and-feather" type of wedge described in the chapter on
limestone. Wedges are of different lengths to accommodate them for
use in deep or shallow holes. Blunt-steel wedges used without feathers
are employed for driving in notches. A small steel wedge that tapers
to a thin edge is known as a "point." This term is applied also to a
tool having a pyramidal point used in finishing the surface of stone.
A short, blunt wedge with a rectangular sledging face and triangular
cross section is known as a "bull wedge."

Use of Wedges in Bed-lifting. — In tight-bedded deposits, when by
means of channel cuts or open joints four free vertical faces are provided
for a large mass of stone, the next step is to free this mass from the quarry
floor. As the bedding in most sandstone quarries is horizontal, this
process of separation is known as "bed-lifting," and the breaks are called
"floor breaks." Wedges are used very generally for bed lifting. Ease
of splitting depends on the rift, but breaks are so easily made in almost
any sandstone that drill holes are unnecessary. In their place notches
are cut into the face of the rock by means of hand picks. The notch is
known locally as a "grip" or "side shear." Its lower face is horizontal
or has a slight upward slant; and the upper face slants sharply downward,
forming a V-shaped cut several inches deep. A sharp steel pick is used
to finish the grip to bring it to a sharp point; otherwise, the end of the
wedge would strike against the solid rock and fail to exert the desired
effective upward and downward pressure. Blunt wedges are placed in
the grip and driven with sledges. In hard-splitting rock or in making an
excessively wide break wedges may be placed almost touching each
other. Occasionally grips are cut on two faces, and the mass is raised
by simultaneous wedging at the side and end.

In making floor breaks for large, circular masses cut out for grind-
stones, wedging in a grip is supplemented by wedging in a single drill

SANDSTONE 89

hole 4 or 5 feet deep passing under the center of the stone. A long
wedge with feathers attached to its extremity is inserted in a drill hole.
When it is driven between the feathers the lifting force is exerted near the
bottom of the hole.

Wedging for Subsequent Breaks on Bed. — The softer sandstone blocks
may be split on the bed by cutting grip holes and driving points in them.
In easy-splitting rock they may be placed 1 to 2 feet apart; in tougher
rock they may be placed close together in a continuous grip.

In the more indurated sandstones pick holes can not be cut readily.
In some quarries it is customary to place a block on edge and split it by
sledging on a ''sett" — a quarryman's term for a square-faced steel tool
held in position by means of a handle. The block is marked at the ends
and struck successive blows along the line of desired splitting until a
fracture is made. Quartzites are usually split by wedging in shallow drill
holes.

Wedging for Vertical Breaks. — In quarries which have open bedding
planes spaced at distances of 5 feet or less, wedging may be largely
substituted for channeling, channel cuts being made only where clearance
is required. If possible, such breaks should be made parallel with the
run of the rock. In some northern Ohio sandstone quarries for making a
cross break in a mass of stone 4 to 5 feet thick quarrymen first drill a
row of holes 18 inches apart. Every third hole is made 4 feet deep and
larger than the others, which are 2 feet deep. Plug-and-feather wedges
are placed in the holes and sledged in succession, beginning at one end
of the line, one blow being given to each of the smaller and two blows to
each of the larger ones. Sledging is continued back and forth along the
line until a fracture appears. Breaks thus made may be 80 or 100 feet
long and 20 to 40 feet back from the face. For thin beds, shallow holes
are adequate.

In heavy beds with a poor run, deep-hole wedging is employed.
Thus, for a bed 5 feet thick holes may be made 43^ feet deep and 1}^ to
23^^ feet apart. Holes of this depth are usually about 1% inches in
diameter at the top and 1 % inches at the bottom and are drilled exactly
in the same plane. To assist in producing a straight break in tough rock
a channel about 2 inches deep is cut with hand picks across the rock
surface in line with the drill holes. Occasionally the holes are reamed,
as in the Knox system of blasting. For deep-hole wedging the long
plugs and feathers used are so constructed that when the plug or wedge
is driven the feathers are forced apart a uniform distance at all points
from top to bottom. Thus the pressure is uniformly distributed through-
out the full length of the wedge and is much more effective than when
exerted at a single point or over only a small part of the drill-hole wall.
Furthermore, a wedge with a long taper exerts great force without heavy
sledging.

THE STONE INDUSTRIES

As soon as a fracture appears chips are broken out midway between
drill holes, and blunt wedges are inserted. By sledging these wedges the
pressure is relieved from the plugs and feathers, and they are removed.
If the mass is not too heavy it may then be moved by steel bars which are
inserted in the drill holes as levers.

In rock with a good run breaks up to 3 feet in thickness may be made
in beds merely by driving points in a row of holes cut with hand picks.
Even in tough rock small breaks may be made by cutting a continuous
grip and driving wedges placed close together.

To assist in making straight breaks wedging is sometimes employed
in conjunction with blasting. A powder charge is placed in a reamed

Fig. 18. — Arrangement of derricks for hoisting blocks from an Ohio sandstone quarry.

hole in the center of a mass of stone. Two wedge holes are drilled, one on
each side of the blast hole midway between it and the edge of the block.
Plug-and-feather wedges are driven into them until considerable strain is
placed on the rock before the shot is fired.

Hoisting. Equipment Used. — Most hoisting at sandstone quarries is
done with derricks consisting of a mast and swinging boom. Portable
types are used for wide and shallow quarries where frequent moves must
be made. A type of stiff-leg derrick used near McDermott, Ohio, may be
moved to a new position in about two hours. When placed in position
the base is loaded with blocks of stone to give it stability. For light
hoisting a power shovel having a boom equipped with a running cable
may be substituted for a derrick. Thus, power shovels which are used

SANDSTONE 91

for stripping operations in the winter and would otherwise be idle all
summer are put to practical use.

Position of Derrick. — For large, deep quarries, such as those near
Amherst, Ohio, many derricks arranged at regular intervals along the
quarry bank are required. The mass of rock worked out from one
position of a derrick is called a "motion." This includes the area covered
by the radius of the boom together with that from which the rock may be
dragged economically. The average area of a motion in one Ohio quarry
is 134 by 61 feet. Figure 18 illustrates a ledge or bench and the series of
derricks used to hoist the stone from it.

Cable Attachment. — Grab hooks, chains, and cable slings are used to
hoist quarry blocks from the pit to the bank. Grab hooks are more
generally used, for they have an advantage over other methods in that a
block may be lifted from a flat position on a quarry floor, whereas
chains or slings necessitate raising it several inches from the floor and
blocking it up in order that the lifting apparatus may be passed beneath
it. Shallow holes are made for the tips of the hooks. For hoisting heavy
blocks two pairs of grab hooks may be used, one being attached near each
end of the block. Some companies prefer chains or slings, as they are
considered more secure than grab hooks. They may be left around
blocks which are hoisted from a quarry and placed on flat cars for trans-
portation to mill or yard. It is then a simple matter to hook into the
chain for unloading, and much time is saved.

Pumping. — Some quarries of the hillside or shelf type are fortunate
enough to have automatic drainage. Even pit quarries may in
exceptional instances be underlain by permeable beds which permit
water to drain away. In those that do not have automatic drainage,
pumps must be installed. If only surface water enters a quarry little
pumping is necessary, except in times of heavy rain or flood, but if
springs are encountered the water has to be removed almost constantly.
For shallow quarries with a drainage basin lower than the floor a siphon
may be used if the lift is less than 30 feet. This method has been
used at Hummelstown, Pa., and in a number of bluestone quarries.
Piston pumps operated by steam, electricity, or gasoline engines, cen-
trifugal pumps, and pulsometers are the types most generally used.

YARD SERVICE

Yard service relates to transportation from quarry banks to mills or
finishing plants or direct to transportation lines where mills are not
operated. It also includes transportation of finished mill products to
railway lines or navigable waters over which they are carried to their
destination.

If mills are close to quarries a yard derrick may take stone from the
quarry bank and deliver it direct to the mill. If mills are at a distance

92 THE STONE INDUSTRIES

blocks are loaded onto cars for transportation. When finishing processes,
such as shaping grindstones or splitting and trimming curbstones, are
conducted outdoors, yard derricks may be employed to handle heavy
rock masses. They are also used to load gang cars, to pile finished
products in the yard, or to load them ready for transportation. A derrick
with a boom which may be swung in a complete circle around the mast
but can not be raised or lowered is convenient for handling material of
small size. The boom is in the form of an I-beam, and a small traveling
crane runs back and forth on it. In some places, locomotive cranes do
the work of derricks. Overhead traveling cranes that are commonly used
in mills may be extended to give yard service.

Transportation of rock from quarries to mills or from mills to shipping
points may require cars and trackage. Haulage may be by gravity or
by locomotives, cables, horses, or mules. Teams and wagons or auto
trucks are also used.

SANDSTONE SAWMILLS AND FINISHING PLANTS

Mills Connected with Quarries. — Although large quantities of sand-
stone are sold to dealers or finishing plants nearly all quarries that
produce building stone, grindstones, curbing, or flagging, except blue-
stone quarries, also operate mills or finishing plants. This association of
activities has certain advantages. For instance transportation expense
of waste rock is avoided, as it is left near the quarry; also the quarryman
understands his rock and can work it most economically.

Mills usually are close to quarries. Even when quarries are at high
levels — for example, those near Empire, Ohio — mills are at the same level,
and finished products are brought down by cable cars. At Sherrodsville,
Ohio, however, the quarry is at a high level, and the finishing plant is at
the foot of the hill.

Sawing. Gang Saws. — Sandstone is sawed mostly with gang saws —
iron blades set in a frame. Sand and water are fed to them as they
travel backward and forward, and they cut by abrasion. Blocks of any
width or slabs of any thickness may be obtained by merely adjusting the
spaces between the blades. The frames are of various widths and lengths,
depending on the sizes of blocks sawed.

Two types of gangs are in common use — the rope feed and the screw
feed. The rope-feed gang is suspended by a steel cable attached to
counterbalance weights. The weights may be so adjusted that the
gangs can exert any desired downward pressure of the saws on the rock.
Thus, constant pressure may be maintained, and the rate of cutting will
be governed by the hardness of the rock. If a hard, flinty mass is
encountered, the rate of descent is reduced automatically until the
obstruction is cut through.

SANDSTONE 93

Screw-feed gangs are fed downward by gears, and although the rate of
downward motion may be regulated, the device is not self-adjusting. If a
flinty mass is encountered the rate of sawing is not automatically reduced,
and if the saw is overcrowded the blade is inclined to run to one side, with
consequent production of an uneven rock surface. The screw feed is
employed on nearly all modern gangs.

The saw blades are carefully adjusted to run straight and true without
any side motion, which may involve adjustment of shafts and bearings,
as well as of the blades themselves.

Abrasives. — Silica sand is the abrasive used most commonly in sawing.
It leaves a smooth surface and causes no staining of the rock. Although
crushed steel and steel shot cut 25 to 50 per cent faster than sand under
similar circumstances, they have some disadvantages. They leave a
much rougher surface, and if the stone is to be used for structural pur-
poses, sand-rubbing of the surface may be required, whereas if sand alone
is used as abrasive this process may be omitted. If the stone is porous,
stains may result from iron rust. Steel abrasive is satisfactory if the
stone is to be used for curbing or flagging, as slight stains have
little consequence. A mixture of sand and steel sometimes is used.

Sand Pumps. — Centrifugal sand pumps are commonly used for
elevating the abrasive to a point above the gangs from which it may be
distributed to the saws for repeated use. A belt with crossbars may be
used to convey the sand to the pump well if the concrete bed beneath the
gangs is too flat to return it automatically. In many mills an air lift is
used. A well deep enough to have about one and a half times as much
pipe submerged as above water level is required. A jet of compressed
air entering at the bottom agitates and aerates the water, causing it to
rise in the pipe and carry the sand with it. The great advantages of an
air lift are its simplicity and the absence of moving or rotating parts,
which are rapidly worn out by sand. At some mills pumps are not
employed, the abrasive being shoveled by hand. Where river sand is
obtainable near by, it may be allowed to escape after one use.

Rate of Sawing. — The rate of sawing sandstone blocks depends on a
number of factors, such as length and number of blades, kind of abrasive
and hardness of the stone. Gangs containing 10 to 15 blades saw average
sandstone blocks 5 to 7 feet long at the rate of 3 to 8 inches an hour when
sand is used, and 6 to 12 inches when steel is used. The rate also is
governed by the nature of the product. For rough material, such as
curbing, saws may be crowded to their maximum capacity, but when
building blocks are being sawed this is not permissible, as it may produce
irregularities on the surface. The more indurated sandstones can not be
sawed profitably.

Gang Cars. — In old-fashioned mills timber beds were provided on
which blocks were placed for sawing. The difficulty encountered and the

THE STONE INDUSTRIES

excessive time spent in loading and unloading the bed led to introduction
of the gang car, which is simply a portable saw bed — a small four-wheeled
car which runs on a track beneath the gang and is braced securely.

Transfer Cars. — In some mills much loss of time occurs in removing
sawed slabs from gang cars and reloading them with blocks ready for
sawing. To reduce the time in which the gang saw is idle the more
modern mills are equipped with "transfer cars" which run on a depressed
track in front of the gangs and are provided with a short section of track
across the top. Thus, a gang car may be run from beneath a gang saw
onto the top of a transfer car and removed very quickly. Another gang
car loaded with a block of stone is held ready on a second transfer car,
which may be shifted quickly into proper position in front of the gang-car
tracks, and a new block is thus placed beneath the saws with little loss of

~ b

•)

: :

b :

: :

: -

Fig.

19. — Arrangement of transfer and gang-car tracks in a sandstone sawing mill,
gang saws; h, gang-car tracks; c, depressed transfer-car track; d, transfer car.

time. The track arrangement is shown in figure 19. At some mills
gang cars are readily loaded and unloaded by derricks or overhead
traveling cranes, and transfer cars are not used.

Other Types of Saws. — While gang saws generally are used for major
cuts, smaller blocks and slabs are usually shaped with other types of
saws. Circular saws with Carborundum teeth have given satisfac-
tory service, even in hard sandstones. Blades mounted with diamond
teeth and set in straightcut gang frames are used to some extent. Dia-
mond circular saws have not given satisfactory service.

Wire saws are used for jointing sandstone mill blocks at McDermott,
Ohio. Blocks are placed on the saw bed in piles about 10 feet wide and 4
to 12 inches high, and thus 12, or more are cut at one time. Sand is
used as abrasive. The saw cuts downward by automatic feed at about
24 inches an hour. It cuts very effectively and to reasonably accurate
dimensions with a tolerance of about one-eighth inch. Wire saws also

SANDSTONE 95

are used very effectively in northern Ohio sandstone mills. Clever
adaptations have been devised for cutting rough columns and even for
blocking out carved work.

Rubbing. Nature of Process. — Rubbing is the process of smoothing
the surface of stone by abrasion. Exposed surfaces of structural blocks
usually require such treatment. Where sand is used as the abrasive in
sawing the resulting surface may be so smooth that rubbing will be
unnecessary. However, where steel is used the surface usually is
scratched and scored to the extent that rubbing is required.

Rubbing Beds. — A rubbing bed consists of a heavy iron disk 10 or 12
feet in diameter, which rotates in a horizontal plane. A block or slab of
stone that requires rubbing is placed on the upper flat surface, and while
the disk rotates the block is prevented from rotating with it. Sand
and water are supplied, and the surface is rubbed or ground to desired
smoothness and uniformity. Rubbing beds also are used for grinding
blocks or slabs to accurate dimensions.

Reuse of Sand. — At some mills sand once supplied to rubbing beds is
carried away without being reused. A more economical method is to
return it to the bed until it is worn out. To accomplish this purpose
the sand is washed to a sink in which the larger particles remain while
the fines are carried away in the water. A bucket elevator or some other
device is used to carry the sand to a point above the rubbing bed.

Planing. — Planers, chiefly of the Scottish reversible-head type, are
used in shaping such forms as cornices, moldings, and curbstones. In
planing the harder sandstones difficulty is experienced in getting a tool
that will stand the work required of it, as the heat generated burns the
steel. Overheating may be overcome by directing a heavy stream of
water on the tool.

Manufacture of Curbing. — The manufacture of curbstones is an
important part of the sandstone industry. The larger blocks usually are
drilled and split into smaller sizes with plug-and-feather wedges. Final
splitting into rough curbstones is accomplished in different ways, depend-
ing upon the ease of splitting. In "split rock" a series of notches are
cut in line by means of a pick, the rock is then marked along the line
with a chisel-edged tool and hammer, and the split is made by sledging
bull wedges in the notches. In rock which splits with greater difficulty
plugs and feathers may be used. Massive rock is sawed into curbing
blocks.

Some Ohio mills are designed especially for manufacture of curbing.
Planers are arranged in two parallel series with tracks between. The
sandstone blocks are brought in on cars and transferred to the planers
with overhead traveling cranes or pneumatic hoists. Finished curb-
stones are reloaded in the same way and conveyed from the mill for
storage or shipment.

THE STONE INDUSTRIES

Manufacture of Grindstones and Pulpstones. — In southern Ohio
the larger grindstones and pulpstones are cut in circular form in the
quarry by means of circle-cutting drills, as described on a previous page.
In northern Ohio they are quarried as rectangular blocks and scabbled
to circular form. Stones thus roughly shaped are finished by cutting
square-center holes, placing them on shafts, and turning them to true
form with steel tools as they rotate. Both faces and sides are trimmed
in this way. Figure 20 illustrates the method of shaping a 7-foot stone.
The upright pins on the timber base are for the purpose of holding the
cutting bar in various positions. A workman may stand on either side,
and if two men are employed both sides of the stone may be trimmed

Fig. 20. — Method of shaping a large grindstone in a lathe.

simultaneously. Grindstone lathes are operated by steam, electricity,
gasoline, or natural-gas engines, the choice of power depending upon
relative costs and availability. Most lathes are provided with suction
pipes in the pits to carry away the dust and thus reduce the danger of its
injurious effects upon workmen.

Smaller stones which are not circular are mounted in lathes and
marked at each side for their proper circumference by holding pointed
tools against them. The grooves are not cut deeply into the rock as
this would involve the danger of masses of rock flying from the stones,
impelled by centrifugal force. While the stones are at rest the outer
masses are broken off with hammers and thereafter the stones are turned
to finished form in the usual way.

Cutting and Carving. — A certain amount of hand cutting is necessary,
especially in plants where building stone is produced. It involves

SANDSTONE 97

rough work, such as the cutting of rock-face ashlar from irregular waste
blocks, and also the finer carving required for decorative effects. Sand-
stones are so variable in character that both methods and tools differ
widely in various localities. For example, a light and springy tool
"plucks" less than a heavy tool in the fine-grained sandstones of McDer-
mott, Ohio. The best methods of cutting and the most efficient tools
to use can be determined only by experience.

Handling of Material. — Stone is a heavy material, and speed in mill
work demands the most efficient types of crane service. Derricks are
sometimes employed, but the overhead traveling crane is handled
more quickly and easily and has a wider range. Pneumatic cranes give
very efficient service for handling the smaller pieces, such as curbstones.
In some Ohio curbing mills a pneumatic crane of 2,000-pound capacity
serves each planer, and other cranes are employed for yard service.

THE BLUESTONE INDUSTRY

Definition of Bluestone. — Bluestone is a commercial name for a
variety of sandstone having properties sufficiently characteristic and
distinctive to justify its recognition as a separate rock type. It may be
defined briefly as an indurated arkose sandstone, most of which splits
easily into thin, smooth slabs. The term was first applied to certain
blue sandstones quarried in Ulster County, N. Y. With the develop-
ment of the industry it was found that stone of similar character was
abundant in various other localities in New York and in Pennsylvania.
Although they differ considerably in composition, size of grain, and color,
all are dense, compact, hard, and usually dark, and, particularly in the
upper beds, split into thin and uniform slabs. The term "bluestone"
therefore is applied to all varieties, irrespective of color. Blue, gray,
red, pink, and greenish colors have been observed.

Composition of Bluestone. — After making a microscopic study of
bluestone from Ulster County, N. Y., Berkey'^ states that the rock
consists of feldspars, quartz, sericite, chlorite, calcite, clay, and a little
pyrite and organic matter. Hornblende and biotite probably were
present in the rock originally but have altered entirely to the more stable
sericite and chlorite. The grains are angular and are held together with
a strong, siliceous cement. Although certain variations in composition
and texture may occur in bluestone from different localities, in general
they are all of this type.

Structural Features. Joints. — Joints usually are in two vertical
systems, nearly at right angles to each other and spaced 5 to 70 feet
apart. Generally the systems are north-south and east-west; the
former are termed "heads" and the latter "sides." Usually joints are

^1 Berkey, C. P., Quality of Bluestone in the Vicinity of Ashoken Dam. Columbia
Sch. Mines Quart., vol. 29, 1907-1908, pp. 154-156.

98 THE STONE INDUSTRIES

straight, though sometimes they are curved and irregular. Moderately
spaced straight joints are of great assistance in quarrying.

Beds and Reeds. — Most bluestone beds lie horizontal or nearly hori-
zontal. Open bedding planes are a few inches to several feet apart,
or in the massive rock may be at 25- to 35-foot intervals. Inter-bedded
shales are common, such rock being termed "pencil" by quarrymen.

The chief characteristic of bluestone is its weak cohesion in certain
well-defined planes, resulting in a strong tendency to split in thin sheets
that parallel the bedding. In the upper beds the partings usually are
developed to such an extent that the rock splits with great ease into
large, thin slabs. At greater depths the partings are less pronounced,
though in most beds the rock may be split easily along certain streaks
termed "reeds," which have already been defined. The presence of
reeds has made bluestone a valuable rock for the production of flagging.

In some deposits or in certain parts of deposits reeds are lacking.
Cross-bedding may be present, or the rock may be massive — a "liver
rock." In some quarries such beds are avoided because flagging can
not be made from them. However, they are the strongest and most
durable and therefore the most valuable for structural purposes.

Run. — In bluestone there is usually one vertical plane in which
splitting is comparatively easy. This is known as the "run" of the rock
or the "free way," and the vertical plane at right angles to it is termed
the "hard way." Fortunately in most deposits the run parallels one of
the major jointing systems, thus permitting easy separation of right-
angled blocks.

Strength and Durability. — Good-quality bluestone is very strong.
Berkeyi^ states that the great strength of the rock is due to the facts that
alteration of the ferromagnesian and aluminous minerals has freed
considerable secondary quartz, which has attached itself to the original
quartz grains, making them more angular and developing an interlocking
texture, and that the secondary fibrous minerals have promoted further
interlocking of the grains.

Bluestone is probably the most durable of any quarried stone except
quartzite. The coarse-grained varieties are somewhat more resistant
to weathering than those of finer grain. The presence of clay in a
bluestone renders it less durable. In natural outcrops of bluestone along
steep hillsides the more durable beds can be recognized easily by their
steep, almost clifflike contour, whereas the softer, more easily weathered
beds outcrop as more gradual slopes. Thus, if the ledge consists of alter-
nate hard and soft beds, the face of the hill will present a series of terraces.

Uses. — Bluestone has been used very widely for sidewalks and flagging.
It is well-suited for these purposes, as it resists wear and does not become

12 Berkey, C. P., Work cited, p. 157.

SANDSTONE 99

slippery. Bluestone with the reeds spaced more widely than in sidewalk
stone is used for curbing, steps, sills, caps, water tables, and coping.
Heavy mill blocks are sawed into forms suitable for the various purposes
mentioned above, or into building blocks. The rock is used to some
extent for floor tile. Various colors may be combined to make attrac-
tive floor patterns or borders. The more massive varieties of bluestone
are suitable for heavy masonry.

Commercial Types. — The primary product of the quarry is marketed
in three forms — flagging, "edge stone," and "rock" or mill blocks.
Flagging is stone from beds that split with remarkable ease into thin,
uniform sheets. Commonly the slabs are 10 by 12 feet and only 2 inches
thick. What is termed "edge stone" splits out in thicker beds and is
dressed for curbing, sills, caps, and coping or other similar uses. " Rock "
or mill blocks are taken from the more massive beds that are not reedy
and are therefore well-suited for structural purposes. Mill blocks are
more valuable per cubic foot than the other forms quarried.

Quarry Methods. Types of Quarries. — Bluestone quarrying differs
from most other types because there are few large operations and many
small ones. Numerous small openings quarried by one to eight men are
operated in summer, some being worked only at brief intervals in connec-
tion with farming or other occupations. The product is hauled by teams
or automobile trucks and sold to stone dealers. Although the quarries
are small, total production amounts to considerable quantities; New
York and Pennsylvania, the chief producing States, normally sell annually
an amount valued at about $1,000,000 at the quarry.

Quarry Equipment. — In many small quarries the equipment is limited
to the necessary tools and appliances, such as crowbars, shovels, hammers,
points, drills, wedges, picks, plugs, and feathers. In numerous quarries
no derricks are provided, the rock being handled by crowbars. Hand-
power or horsepower derricks are common, though steam or gasoline
engines are employed in some places. Some derricks are provided with
gears giving two speeds, a rapid speed for light loads and a slow speed for
heavy loads. Some of the larger quarries have compressed-air plants for
operating drills. For drainage purposes steam or gasoline pumps or
pulsometers are operated in a few places. In others, siphons are employed,
and in many quarries conditions favor automatic drainage. A black-
smith shop for sharpening and shaping tools is a necessity at every quarry.

Separation of Larger Masses. — When vertical seams occur in two
systems at right angles to each other and 10 to 30 feet apart they are of
great assistance in quarrying, and the quarryman endeavors to work to
these seams wherever possible. Where seams are far apart artificial
cross breaks must be made, a process known locally as "snubbing,"
which usually is accomplished by drilling holes about 6 feet apart and
blasting by the Knox method, as described on a previous page. The

100 THE STONE INDUSTRIES

masses thus separated may be 15 or 20 feet in lateral dimensions and
1 to 3 or 4 feet thick depending upon the spacing of the open-bed seams.
Another method less commonly used is to drill a row of holes 1 or 13^
inches apart and to broach out the cores between them, making a
continuous cut.

Cross Breaks. — For smaller cross breaks, particularly those in thin-
bedded rock, the wedging method is employed. In drilling wedge holes a
"starter" and a ''follower" are sometimes used. The starter drill is
commonly l^i inches in diameter and drills only the upper 13^^ inches of
the holes. Then the follower, a drill of J^ inch diameter, finishes the
holes. In the process of wedging in such holes the pressure of the plugs
and feathers comes at a point some distance below the surface of
the rock, whereas if the holes are of the same size throughout their full
depth the pressure is inclined to be excessive near the surface, causing
the rock to shell off. A row of pick holes along the line helps to make a
straight break. Wedge holes may be spaced considerably farther apart
when splitting parallels a pronounced run than when a break is made
parallel with the hard way.

For separation of large masses blasting sometimes gives better results
than wedging. A charge of black blasting powder fired in a single
reamed hole may make a straight break 12 to 18 feet long and 3 to 4 feet
deep. In many quarries it is customary to blast the rock parallel with
the run and to wedge it the hard way.

Splitting Beds. — In rocks in which the reeds are pronounced, beds are
easily split by wedging, but more massive rock, with greater difficulty.
A typical method is to cut notches about }^ inch deep and 3 inches apart
across both ends and along one side of the block. A fracture is started
by driving points into the holes successively first at one end of the block
and then at the other end. When a fracture is formed some distance from
each end thin wedges are driven into it at both ends and on the edge.
The block is then turned down and started on the opposite edge, and the
fracture is completed by wedging. When the process is thus carefully
conducted it gives a uniform fracture. A bull wedge sometimes is used in
splitting curbstones.

Trimming. — There is usually need of trimming edges, especially
where such products as curbstones, steps, and coping are made. Where
curved corner curbstones are made much trimming is necessary.
With careful handling two corner curbs may be broken from a single
block by making a curved break. The amount of trimming required is
influenced by cross bedding, which may result in oblique splitting of
beds. If a slab for curbstones is thicker at one edge than the other, it is
"pitched off" with a hand tool and hammer, a process that wastes rock
and requires much time and labor. When trimming is done in the
quarries hand tools and hammers generally are employed.

SANDSTONE 101

Marketing Bluestone. — Operators of the many small bluestone
quarries sell their products to stone dealers, or dealers may operate the
quarries themselves. They have yards termed "docks," situated on
navigable water or railway lines, where stone from the quarries is unloaded
and shipped by rail or water to its destination. The docks almost
invariably are equipped with derricks. Transportation is usually by
wagons and trucks, as very few quarries have railway sidings. The cost
of transportation is borne by the quarryman and ranges from 8 to 50
per cent of the value of the stone, depending on the haulage distance and
the condition of roads. Structural stone is sold to building contractors,
and curbing and flagging to street-construction contractors, highway
boards, or municipalities.

WASTE IN SANDSTONE QUARRYING AND MANUFACTURE'

Cause of Waste. — Even in sandstone deposits of the highest quality
much rock is either unsuitable for use or is wasted in quarrying
and manufacture. Much of the waste may be due to imperfections in the
rock, over which man has no control. Joints may be irregular or closely
spaced, or they may intersect at sharp angles. Bed seams may be close
together or wavy and uneven, or the rock may be cross-bedded, with
intersecting bed seams. The texture may be uneven, and the degree of
cementation may lack uniformity. Iron compounds may cause stains,
and the presence of clay may increase the absorption. Such defects in
composition and structure may bring about the rejection of many blocks
of stone.

Much serviceable rock is wasted in quarrying and milling. Excessive
blasting with unnecessarily heavy charges, the ''stunning" of channeling
machines, and improper wedging are common causes of excessive waste.
Even in the best-conducted quarries and mills part of the good stone must
be cut and trimmed away to fashion blocks and slabs to their required
shapes and dimensions. Therefore, the volume of finished products
may be less than one-half of the gross quarry output.

Waste Utilization. — Sandstone is chemically inert, and its waste
products therefore have much more limited application than waste lime-
stone or marble. However, the economical quarryman seeks to cultivate
certain fields of utilization to win some profitable return from at least
part of his waste material. Heavy, irregular blocks of sandstone unsuit-
able for other use may be used for shore protection along rivers, for
spillways at dams, or for the construction of harbor breakwaters. Irregu-
lar small fragments which have one good face are used to some extent as
rubble, though rubblestone has been displaced by concrete quite generally
during recent years. Waste blocks may also be trimmed to suitable
sizes and shapes for regular course or broken ashlar walls. Waste sand-
stone may be crushed for concrete aggregate. As a rule, sandstone is not

102 THE STONE INDUSTRIES

suitable for road surfaces, although some argillaceous sandstones contain
enough binding material to render them satisfactory. Some quartzites
are used for road surfaces where traffic is heavy. Sandstones are more
suitable for road bases, as they provide good drainage and cushion,
and a market for waste is found in this field.

Sand is an important by-product at many sandstone plants, especially
where the more friable types are worked. The sand may be used for
sand-lime brick manufacture, for mortar, for furnace floors, or as engine
sand. The utilization of pulverized sandstone as asphalt filler is receiv-
ing some attention.

Prevention of Waste. — In view of the limited number of uses for
which waste sandstone may be employed, quarry operators endeavor to
keep the proportion of waste at a minimum by quarrying in accordance
with joint systems and other rock structures, by exercising great care in
blasting, by employing skill and good judgment in wedging, and by
careful selection of rock that it may be suitable for its intended use.
Waste may be reduced by skillful milling. Blocks containing streaks
or spots may be cut in such manner that the blemishes do not appear
on exposed surfaces. There is an advantage in operating a mill in con-
nection with a quarry, for the quarryman understands his rock and can
therefore cut it to much better advantage than a millman unacquainted
with its peculiarities.

Bibliography

AuBURY, Lewis E. The Structural and Industrial Materials of California. Cali-
fornia State Min. Bur. Bull. 38, 1906, pp. 114-116.
Bowles, Oliver. Sandstone Quarrying in the United States. U. S. Bur. of Mines

Bull. 124, 1917, 143 pp.
BowNOCKER, J. A. Building Stones of Ohio. Geol. Survey of Ohio, 4th ser., Bull.

18, 1915, 160 pp.
Eckel, E. C. Building Stones and Clays. John Wiley & Sons, Inc., New York,

1912, pp. 127-149.
Galliher, E. Wayne. Geology and Physical Properties of Building Stone from

Carmel Valley, California; Mining in California. California Dept. Nat. Res.,

Div. of Mines, January, 1932, pp. 14-41.
Richardson, Charles H. Building Stones and Clays. Syracuse Univ. Book Store,

Syracuse, N. Y., 1917, pp. 229-266.
Stone, R. W. Flagstone Industry in Northeastern Pennsylvania. Pennsylvania

Bur. Topog. and Geol. Survey Bull. 72, 1923, 7 pp.
Building Stones of Pennsylvania. Pennsylvania Topog. and Geol. Survey

Bull. M15, 1932, 316 pp.

CHAPTER VIII

GRANITE
GENERAL CHARACTER

As pointed out in the discussion of rock classification, granite is of
igneous origin, coming up from unknown depths; thus, except in rare
instances, it may be rehed upon to extend downward far beyond the
possibihty of economical quarrying. Granites and related rocks are
the hardest of all ordinarily used for structural purposes and the most
difficult and expensive to quarry and shape into finished forms. The
many troublesome problems that confront the granite quarryman have
stimulated his inventive genius to devise new and better ways of winning
this important structural material from the earth and fashioning it
into useful and attractive products. The technology of granite is
therefore, of unusual interest.

MINERAL COMPOSITION

Chief Minerals. — The essential constituents of granite are feldspars,
quartz, and either mica or hornblende; and their proportions vary
greatly. According to Merrill, ^^ one European granite contains 52 per
cent feldspars, 44 per cent quartz, and 4 per cent mica; another contains
35 per cent feldspars, 59 per cent quartz, and 6 per cent mica. Granites
as high in quartz as these are very difficult to work, but few quarried in
the United States have as large a proportion as these foreign granites.
The red granite of St. Cloud, Minn., contains 70 to 80 per cent feldspars,
15 to 20 per cent quartz, and 5 to 10 per cent combined mica and horn-
blende. Dale^* found that a Hardwick (Vt.) granite contains about 62
per cent feldspars, 22 per cent quartz, and 16 per cent biotite mica. He
also states^^ that dark Barre granite contains about 65 per cent feldspars,
27 per cent quartz, and 8 per cent mica.

A simple method of determining the proportions of the chief constit-
uent minerals is described by Dale.^** A network of lines intersecting at
right angles is traced on the polished surface of granite and spaced at
such intervals that no two parallel lines will traverse the same mineral

1^ Merrill, G. P., Stones for Building and Decoration. 3d ed., John Wiley & Sons,
Inc., New York, 1910, p. 46.

1* Dale, T. Nelson, The Commercial Granites of New England. U. S. Geol.
Survey Bull. 738, 1923, p. 110.

1* Work cited, p. 124.

" Work cited, p. 100.

103

104 THE STONE INDUSTRIES

grain. The total length of the lines is measured, the diameters of all
the particles of each mineral variety are added separately, and their
proportion to the total length of the lines is calculated.

Feldspars are the most conspicuous and ordinarily the most abundant
minerals in granites. Several kinds usually are present. The potash
feldspars (microcline and orthoclase) are the most prevalent and are
generally accompanied by small percentages of one or more members of
the lime-soda group (the plagioclases). Feldspars may be white, gray,
opalescent, reddish, brown, or green, and the prevailing color determines
to a large extent that of the rock. Quartz grains may be recognized
readily by their glassy luster, absence of cleavage, and uneven fracture
surface. Quartz is commonly clear and transparent but may be milky,
bluish, yellow (citrine), opalescent, purple, or smoky. Next to the
feldspars and quartz, black mica (biotite) is the mineral most abundant
in a majority of granites; dark green or black hornblende may be nearly
as abundant ; and muscovite frequently occurs. When large percentages
of biotite or hornblende are present the rock may be nearly black.

Accessory Minerals. — Accessory minerals are those that may or
may not be present in a rock. When present they are usually in sub-
ordinate amounts, and some may be detected only with a microscope.
Garnet, zircon, epidote, titanite, magnetite, hematite, limonite, ilmenite,
pyrite, apatite, augite, and rutile are the more important accessory
minerals of granite, and minute quantities of many others may occur.

CHEMICAL COMPOSITION

The chemical composition of granite has little economic significance.
Many prospective granite-quarry operators wish to have samples of
their rock analyzed to determine its quality and probable value, failing
to realize that any one element or compound may form constituent
parts of several different minerals, some of which may be desirable and
some undesirable. For example, an analysis may show a certain amount
of iron, but without a very complete analysis and careful calculation the
amount of iron present as a constituent of a stable biotite or hornblende
or of an unstable and detrimental pyrite or garnet can not be determined.
A chemical analysis, however, may indicate the general composition;
thus a high silica content would indicate a high percentage of free quartz.
Analysis of a granite is therefore much less important than determination
of its mineralogical composition.

PHYSICAL PROPERTIES

The adaptability of a granite for structural or ornamental use is
governed mainly by its physical properties, the character of its con-
stituent minerals, and their grouping.

GRANITE 105

Texture. — The texture of granite signifies the size and arrangement of
mineral grains. Uniform grain size usually is demanded in commercial
granites for building or ornamental uses. Lack of such uniformity
condemns thousands of deposits throughout the world for practical use.
Grain size varies greatly in different granites. They accordingly are
classed as fine-, medium-, and coarse-grained. Medium-grained granites
are those in which the feldspars average about one-fourth inch across.

Uniform distribution of the minerals is as important as uniform
grain size. Light and dark minerals should be distributed evenly
throughout the rock mass, for this gives uniform color and texture.
Many commercial deposits display remarkable homogeneity; the rock
may not vary in color or texture for many feet, either vertically or
horizontally. A number of granite enterprises owe their success to such
consistent qualities.

Color. — The color of a granite is governed largely by that of the
feldspar, usually the most abundant mineral. However, it may be
modified to some extent by the quartz, hornblende, or mica, if consider-
able amounts are present. White, light gray, dark gray, pink, red, and
olive-green commercial granites are common. Uniform color distribu-
tion is a desirable feature.

Hardness. — The hardness of a granite is determined by that of its
constituent minerals. As feldspar and hornblende have a hardness of
about 6, and quartz of 7, all granites must be exceedingly hard. Those
having abundant quartz are the hardest. Some are quite brittle and
shatter readily, while others have interlocking grains that make them
very tough and consequently difficult to separate by blasting or wedging.

Porosity. — Although freshly quarried granite appears very dense and
impervious to moisture, investigations by Merrill, Watson, Buckley,
Parks, and others show that the pore space of average granites is 0.10 to
0.50 per cent. These microscopic pores are both within and between
the mineral particles. Dale^^ states that an average granite contains
0.8 per cent water and can absorb about 0.2 per cent more; that is,
1 cubic yard of granite weighing about 2 tons contains about 33^^ gallons
of water and if immersed can absorb nearly 1 gallon more.

Although the total pore space is very small it may have interesting
effects. Pores of subcapillary size do not give up their water content
readily and damage from frost action may result. As will be shown later,
the fluidal cavities in quartz probably bear definite relation to the rift.

VARIETIES

Granites generally are named from the most prominent ferro-mag-
nesian mineral present; thus, they may be called "biotite granites,"
"hornblende granites," or, more rarely, "augite granites." If two such

" Work cited, p. 12.

106 THE STONE INDUSTRIES

minerals are prominent a compound word may be used, as "hornblende-
biotite granite." The name "binary granite" is sometimes given to one
consisting only of quartz and feldspars. Sometimes granites are named
from an unusually prominent accessory mineral, as "epidote granite"
or "tourmaline granite." Classification by color provides for red,
gray, white, or other groups.

Granites are also classed according to texture. They may, for exam-
ple, be designated "fine-grained" or "coarse-grained." "Porphyritic
granite" consists of relatively coarse grains in a fine-grained groundmass.
The term "aplite" is usually applied to a fine-grained, light-colored
granite that occurs in dikes. A rock may have the mineral constituents
of a granite but show a banded arrangement of light and dark minerals,
owing to folding while the rock was plastic or semimolten. Such meta-
morphic rocks (gneisses) are classed commercially with the granites and
may be designated "gneissic granites."

RELATED ROCKS

Granite is only one of many igneous rocks, but it occupies so promi-
nent a place in any discussion of dimension stone that the other less
important types are included with it. When igneous rocks are considered
for building and similar purposes granite predominates for two reasons.
First, there are few other igneous rocks of composition, texture, or color
suitable for structural or ornamental uses. Second, most igneous
rock types so employed are classed commercially as granites, even though
some are far removed petrographically.

Certain related varieties are logically classed with granites, as they
are so similar as to be distinguishable only by very careful examination,
sometimes only by the use of a microscope. The more prominent of
these closely related types are syenite, diorite, quartz diorite, and
quartz monzonite.

Other rocks classed commercially as granites differ sharply from them.
The most important of the distantly related types are the so-called
"black granites," which may be gabbros, diabases, or dark diorites.
They are similar to true granites in structure and texture but consist
essentially of plagioclase feldspar and augite, with little or no quartz.
Some are quite ornamental, will take a high polish, and are used in the
same way as granites. Rhyolites and volcanic tuff, uses of which are
limited, also are distantly related to granites.

STRUCTURAL FEATURES

Certain structural features affect both the quality and workability
of granite. Joints, sheet structure, rift, grain, dikes, knots, and hair
lines are the most important.

Joints. — Joints, or seams, are natural fractures that traverse the
granite mass, usually in a nearly vertical direction. Pynamic geologists

GRANITE

107

generally agree that they are caused by compressive or torsional strain,
which has been resolved into two components, each at an angle of about
45° with the direction of strain. This theory has some confirmation in
the fact that joints occur quite generally in two main systems, called
"major" systems, which intersect at about 90°; less prominent systems
are termed "secondary." Joints may have resulted from a constant
force exerted in one direction over a wide area, for the systems tend to
run in the same compass directions in many quarries throughout an
extended deposit. Thus, in the St. Cloud (Minn.) region, where the

Fig. 21. — Strike of major and secondary joints in granite deposits near St. Cloud, Minn.

writer some years ago took numerous compass readings, most of the
major joints strike either approximately north and south or east and
west, as shown diagrammatically in figure 21.

Major systems are common in granite deposits, but many inter-
mediate and irregular joints may occur, and in some deposits no sys-
tematic arrangement may be evident. Obviously an arrangement in
two parallel systems meeting at right angles, with few intermediate or
irregular joints, is the most favorable for quarrying, as it facilitates
removal of blocks and maintains a low percentage of waste.

The spacing of joints is extremely variable. If they are only a few
inches apart the rock is useless as dimension stone, except possibly for
small rubble. Straight major joints 10 to 30 feet apart usually are
regarded as advantageous in quarrying. If only 3 or 4 feet apart, blocks
of sufficient size may be obtainable, but the rock may be stained by
weathering agencies acting from the joint walls. Such staining detracts
from its quality for memorial uses but may be an asset for certain archi-

108 THE STONE INDUSTRIES

tectural effects now in demand. In some localities, such as the Lithonia
district of Georgia and the Mount Airy region of North Carolina, the
rock may be sound and massive over wide areas without any joints.

Sheeting Planes. — Sheeting planes are approximately horizontal
partings that separate a granite mass into sheets or layers. They
generally parallel the rock surface and are consistently closer together
near the surface than at depth. In some granites they are very promi-
nent and closely spaced. On Crotch Island, Me., they are only 2 to
4 feet apart near the surface and present, although more widely spaced, at
a depth of at least 140 feet. Widely separated sheeting planes occur at
a depth of 250 feet at Quincy, Mass. In the St. Cloud district, Minne-
sota, they are few and widely separated. As a rule, they are more closely
spaced than joints in New England, while the reverse is true in Min-
nesota. On this account quarrymen who have worked both in New
England and in the St. Cloud district describe the rock of the latter
region as "standing on end." Just as the granites of Lithonia, Ga., and
Mount Airy, N. C, are crossed by few joints, so are they without sheet
structure. In such deposits artificial sheets must be forced in the process
of quarrying.

The origin of sheeting planes is obscure. Dale^^ discusses in some
detail all the theories advanced, concluding that compressive strain
was probably the main factor in producing them, though expansion under
solar heat may have been a contributory cause in the surface layers.
The arched structure commonly found in sheeting planes may account
for the conspicuous domelike form that characterizes many granite
deposits.

Rift and Grain. — Many granites split in some directions with greater
ease than in others. The direction of easiest splitting or the fracture
system that makes splitting possible is called the "rift." A second
less strongly marked fracture system may stand at right angles to the
rift. It is generally called the "grain," but in Minnesota it is called
the "run." The direction at right angles to both rift and grain is
called the "hard way" or "head grain."

In Minnesota the rift is nearly always horizontal, and the grain in
some vertical plane. In many Vermont and Maine quarries conditions
are reversed, the grain usually being horizontal and the rift vertical.
In New Hampshire conditions more nearly resemble those in Minnesota.
There are many variations, but one direction of comparatively easy
splitting is almost invariably horizontal and the other at right angles to it.
The direction of grain may be constant over a wide area. Thus, through-
out central Minnesota the grain like the major joints is predominantly
north and south, except in one small area where it is east and west.

18 Work cited, pp. 26-36.

GRANITE 109

The origin of rift and grain, like that of sheeting planes, is obscure.
They are apparently independent of sheets and of flow structure. Ac-
cording to Dale they are caused principally by orientation of the minerals
— that is, by the arrangement of the minerals in lines or planes or with
parallelism in their cleavage directions. They may also be caused by
the arrangement of fluidal cavities in parallel planes in the quartz grains;
by incipient jointing caused by strain; or by microscopic faults or frac-
tures. That rift and grain in the granites of central Minnesota originated
in orientation of minerals is indicated rather definitely by two facts:
First, the rift surface is smoother than other surfaces. A skilled paving-
block cutter can detect the rift blindfolded by the feel of the surface.
This condition would indicate predominance of feldspar cleavage faces
parallel to the rift. Second, some quarrymen have stated that they
recognize the rift by "the direction in which the grains point." They
appear to base their observations rather on the dark than on the light
minerals.

Some granites display no evidence of rift or grain. Even in rocks
in which they are most fully developed rift and grain are obscure proper-
ties that may be recognized only by a skilled stonecutter. Nevertheless,
they are of the utmost importance in quarrying, as they make splitting
easy and give comparatively smooth, uniform surfaces. Paving-block
cutters are exceptionally skilled in recognizing rift. It may be safely
said that the granite paving-block industry could not exist were it not
for rift and grain in the rock.

Dikes. — Dikes are defined as fissures filled by mineral matter injected
in a plastic to fluid condition. Dike material is of two main types —
acidic or basic; that is, it may be siliceous, like granite, or may contain
a large percentage of ferromagnesian minerals, thus having the composi-
tion of a basalt or diabase. Dikes in granite deposits may range in
width from a fraction of an inch to several feet and occasionally to 50
or even 150 feet.

Acidic Dikes. — Some dikes consist of granite which differ radically
from that into which it is injected. In Minnesota, red granite dikes
commonly traverse gray granites. The well-known granites of Westerly,
R. I., are quarried in a formation that has been interpreted as a great
dike 50 to 150 feet thick. The occurrence of commercial granite in dike
form is quite exceptional.

Aplite dikes — fine-grained, light-colored granite — are very common.
They are usually quite narrow, and their fine-grained texture probably
is due to comparatively rapid cooling caused by contact with the previ-
ously solidified rock masses on either side.

Pegmatite, according to Hess,^* is a general name for rocks with
coarsely and unevenly crystallized segregated minerals occurring as

19 Hess, Frank L., Pegmatites. Econ. Geol., vol. 28, no. 5, 1933, pp. 447-462.

110 THE STONE INDUSTRIES

dikes, veins, or metamorphic masses. During their formation the
constituents of ordinary granite were supplemented by water vapor and
numerous volatile elements, such as fluorine, chlorine, boron, phosphorus,
and sulphur. A slow process of crystallization and mineral replacement
caused large crystals of feldspar, quartz, and mica to form, and associated
with them in many places was a series of characteristic pegmatite min-
erals, such as tourmaline, scheelite, garnet, cassiterite, apatite, and beryl.

Pegmatites supply practically all the feldspar and sheet mica of
commerce but have little value as sources of structural or ornamental
stone.

Basic Dikes. — The more common types of basic dikes are those
termed "diabase" or "trap" dikes. They are dark green, dark gray,
or black, are very hard and dense, and are common in many granite
regions. More than 360 have been counted in the Rockport quarries,
Cape Ann, Mass.

Effect of Dikes on Granite. — Granite traversed by dikes of any kind
rarely is utilized as dimension stone. Basic dikes, particularly, stand
out as dark, conspicuous bands that mar the appearance of the stone.
They are unwelcome in quarries because of the time and labor wasted in
removing them and of the granite they render valueless commercially.
It has also been observed that rock near dikes tends to be unsound.
Such a condition is to be expected, because the shattering which formed
the open fractures into which the dike material was injected may have
developed fine cracks or incipient seams in the near-by rock.

In some deposits, however, granite close to dikes, though not actually
cut by them, may be of good quality. The heat of the dike material
may have developed minute cracks in the quartz and feldspar of the
adjoining granite, but this contact effect may not extend beyond a depth
of 1 or 2 inches.

Knots. — The term "knot" is applied to a circular, oblong, or irregu-
lar mass that commonly occurs in a granite otherwise of uniform texture.
Knots are usually dark and are regarded as serious blemishes, par-
ticularly on polished surfaces, where they stand out like blots on a sheet
of paper. As they in no wise affect strength or durability, stone con-
taining them may be used for curbing, paving, or other purposes where
color means little. Knots are of two kinds — segregations and inclusions.

The more common types are segregations — groupings of dark minerals
in spots during cooling and solidification. Segregations consist of the
same minerals as the parent rock; but the dark minerals, hornblende
and biotite, are more abundant than the light quartz and feldspar. Both
the origin and distribution of segregations are difficult to explain. No
conclusions have been reached regarding their occurrence, and the
probability of their presence or absence in any locality is a matter of mere
speculation.

GRANITE 111

Knots designated as "inclusions" are masses of foreign material
caught up by a semiliquid magma and held within it until the whole has
solidified. Such knots are somewhat angular and comprise material
different from the rock in which they are inclosed. As inclusions consist
of foreign materials they are most apt to occur near the borders of granite
masses — that is, in the zones nearest contact of the granite with other
rocks.

Methods of Distinguishing Knots. — As noted previously, some rules
can be laid down for the occurrence of inclusions, but none have been
established for segregations. At times, therefore, it is rather important
to interpret the origin of knots and classify them correctly. A specific
example best illustrates the method of interpretation. In a certain
granite two types of knots occur. Microscopic examination in thin
section reveals that one consists of orthoclase, plagioclase, quartz, and
biotite, the same minerals that occur in the surrounding rock, though the
proportion is different, biotite being in excess. These minerals have the
same peculiarities as corresponding minerals in the main rock mass; for
example, the biotite contains inclusions of apatite and zircon, a condition
characteristic of this granite. Such knots are undoubtedly segregations.
The other type of knot is quartz and biotite, with no feldspar. The mica
flakes show parallel orientation and have no inclusions of apatite or
zircon. Therefore, the minerals have different characteristics from
corresponding minerals in the surrounding rock, and their character and
arrangement suggest the probability that the knot is an inclusion of
biotite schist. The shape of knots is also indicative of their origin,
angular knots being inclusions and ellipsoidal or spherical knots more
probably segregations.

Hair Lines. — The term "hair line" is applied in some regions, par-
ticularly in Minnesota, to all fine lines of discoloration in granite. These
lines are practically unrecognizable on rough or tooled granite and
therefore are objectionable only on polished surfaces, where they stand
out quite prominently and detract greatly from appearance. Some
black hair lines appearing in granite close to trap dikes are really minute
dikes; others are very small veins filled with dark or smoky quartz.
Green hair lines, consisting of epidote veinlets, are common. If they
follow joint systems they are unimportant, but if they wander irregularly
they may mar the stone. Quarrymen examine rock very carefully for hair
lines before selecting it for monumental purposes. They can be observed
best if water is thrown over the surface.

USES

Dimension granite is used for five principal products. These are, in
order of their production value: Monumental stone, building stone,
paving blocks, curbing, and rubble. Only stone of the highest quality is

112

THE STONE INDUSTRIES

used for monuments, because much of it is polished and polishing empha-
sizes all defects. Increasing quantities of polished granite are being
used also for structural purposes, not only because it is attractive, but
because it is easily cleaned and is not soiled so quickly as unpolished
granite; therefore, highly ornamental stones, as well as the more
ordinary types, are used for building. For paving blocks and curbing
appearance is less important.

The following table, compiled by the United States Bureau of Mines,
indicates the amount and value of granite sold for various uses.

Granite Sold or Used by Producers in the United States, 1936 and 1937,

BY Uses

Use

1936

Juantity

Value

1937

Quantity

Value

Building stone (rough and dressed), cubic feet.

Approximate equivalent in short tons

Monumental stone, cubic feet

Approximate equivalent in short tons

Paving, number of blocks

Approximate equivalent in short tons

Curbing, linear feet

Approximate equivalent in short tons

Rubble, short tons

2,619,700

217,070

2,478,380

203,610

6,826,333

70,500

1,189,680

98,220

77,450

Total value.

2,629,090
6,440,878

702,828

1,206,113

117,835

$11,096,744

3,322,830

274,930

2 , 657 , 630

218,400

7,866,994

73,770

881,310

72,790

111,440

$ 3,068,155

6,628,447

780,611

825,148

149,958

$11,452,319

The corresponding total for 1929 was $25,369,396 and for 1932,
$11,743,408.

DISTRIBUTION OF DEPOSITS

Granites are quarried in many parts of the United States, but the
principal deposits may be grouped in four chief areas, as follows: (1) The
Appalachian district of eastern United States, from Maine to Georgia;
(2) the Middle Western States, particularly Minnesota and Wisconsin; (3)
the Rocky Mountain States, where deposits have not been developed
extensively; and (4) the Pacific Coast States, particularly California.
The general distribution of granites in the United States is shown in figure
22. The leading producing centers for monumental granite are Barre,
Vt., Quincy, Mass., and St. Cloud, Minn. In order of production value
of monumental stone in 1928 the 10 leading States were Vermont,
Minnesota, Wisconsin, Massachusetts, California, Georgia, Rhode Island,
North Carolina, New Hampshire, and Maine, which produced about 86
per cent of the total. The 10 leading States in order of production value
of building stone for the same year were Massachusetts, Minnesota,

GRANITE

113

■5

■w

1*5

■r^

■2

■o

."t;

"o"

.S "^

.2 ®

114 THE STONE INDUSTRIES

North Carolina, New York, New Hampshire, Maine, Georgia, Mary-
land, Pennsylvania, and Vermont. The totals and relative standing
of the States vary from year to year. Figures may be obtained from the
U. S. Bureau of Mines, which annually publishes complete statistics by
States and uses.

INDUSTRY BY STATES

About 96 per cent of the production value of granite dimension stone is
confined to 16 States, which may be arranged in two groups, those of
major importance as producers and those less important. The first
group, comprising the following States, listed in order of production in
1928, furnished about 81 per cent of the total quantity for that year:
Vermont, Massachusetts, Minnesota, North Carolina, Maine, Georgia,
Wisconsin, and New Hampshire. The second group, accounting for
about 15 per cent of the total production, included New York, California,
Maryland, Rhode Island, Connecticut, Pennsylvania, South Dakota, and
Texas.

The order of arrangement of the States and much of the statistical
data given in the following pages are based on 1928 production because
a fairly complete analysis of the 1928 figures has been published. -°

Principal Producing States

Vermont. — Vermont, with an output valued in 1928 at $4,227, 525, or
17.1 per cent of the total for block granite in the United States, is the
largest producer in the country. It specializes in monumental stone, a
material that accounts for about 96 per cent of the total value of granite
produced in the State. About 36 per cent of the monumental stone of the
United States was produced in this State in 1928. The total output in
1929 was valued at S4, 113,886, in 1930 it was $3,348,938, in 1936, $2,238,-
724, and in 1937, $2,511,986.

In this and in most of the States the granites are described briefly by
counties in alphabetical order.

Caledonia County. — The Newark rock is a coarse-grained, light
pinkish gray biotite granite marketed as "Newark pink." The Kirby
Mountain granite, which is bluish gray and medium- to fine-grained, has
been worked to a limited extent. The Hardwick granites, which are
fine to medium, even-grained and bluish gray, are well-known to the
monument trade as "Hardwick" and "Dark Blue Hardwick." Typical
"Ryegate" granite, also known as "Vermont gray," is a medium-grained,
light gray stone suitable for monuments or building. Stone of a decided
blue-gray, "Vermont blue," is quarried at Groton.

20 Bowles, Oliver, and Hatmaker, Paul, Trends in the Production and Uses of
Granite as Dimension Stone. Rept. of Investigations 3065, Bur. of Mines, 1931, 21 pp.

GRANITE 115

Orleans County. — The rock at Derby is a fine-grained, light bluish
gray biotite-muscovite granite, sold chiefly for monuments and monu-
ment bases under the trade name "Derby Gray." Sheeting planes are
3 to 18 feet apart, and one set of vertical joints provides a heading at the
north wall of the quarry. Quarrying was begun about 1880.

Washington County. — The district surrounding Barre and Graniteville,
Washington County and Williamstown, Orange County is the most
important monumental granite-producing center in the United States.
The granite occurs in two prominent domes. Cobble Hill and Millstone
Hill; the latter supplies most of the commercial stone. The two hills
are regarded as parts of a single mass appearing at or near the surface in
an area 4 miles long and 23-^ miles wide. The rock is a fine- to medium-
grained gray to white biotite granite ; the various shades are designated as
"white Barre," "light Barre," "medium Barre," "dark Barre," and
"very dark Barre." The darker varieties are most in favor for monu-"
ment dies and the lighter for buildings, mausoleums, and monument
bases. An average sample of dark Barre granite consists of about 65
per cent feldspars, 27 per cent quartz, and 8 per cent mica.

Sheeting planes 6 inches to 30 feet apart are present in some quarries;
in others they are spaced more widely or are absent. Masses 40 to 80
feet thick without sheeting planes have been encountered. This incom-
plete development of sheet structure makes quarrying difficult. Joints
are irregular, following at least five different compass directions. The
spacing also is quite variable, ranging in most quarries from 1 to 50
feet and in others from 100 to 200 feet. Black knots rarely occur. Its
remarkably uniform texture is one of the chief assets of Barre granite.
The rift ranges from 85° to vertical and varies somewhat in direction,
on Millstone Hill from N.30°E. to N.60°E., and on Cobble Hill from
N..50°E. to N.75°E. Almost invariably the grain is horizontal. Peg-
matite, aplite, and basic dikes occur but are not numerous.

For many years a dozen or more large companies operated quarries
in this district. Recent consolidations have reduced the number, though
the extent of operations has not been curtailed.

Monumental stone is the chief product. The industry consists of two
distinct branches — quarrying and manufacturing. Some quarry compa-
nies also manufacture ; but most of them produce rough blocks only, which
they furnish to neighboring manufacturing plants and ship to all parts
of the country. Figures compiled by the Barre Granite Manufacturers'
Association show that the quarries of the district produced 1,549,443
cubic feet of rough stock in 1928. Of this amount, 1,239,554 cubic feet
were manufactured in the district and 309,889 cubic feet shipped as
rough blocks. More than 100 plants for the manufacture of granite
products are situated in and about Barre, Montpelier, and neighboring
towns.

116 THE STONE INDUSTRIES

Woodbury granite occurs in numerous outcrops within an area about
33^ miles square occupying the northeastern part of the town of Wood-
bury. The principal quarries are on the southeast flank of Robeson
Mountain where several types of dark to light bluish gray biotite granites
occur. Most of them are porphyritic in texture, with large, scattered
feldspar crystals. The products are known to the trade as ''Woodbury
Gray," "Imperial Blue," "Woodbury Bashaw," and "Vermont White."
They are used for both building and monumental purposes. Woodbury
has produced more building granite than other Vermont quarries, except
possibly those at Bethel.

The Cabot granite is dark bluish gray and of fine, even-grained texture.
It is used for monuments and markers. Quarries at Calais, or more
properly at Adamant, are in a ridge of attractive fine-grained, light gray
biotite granite sold as monumental stone.

Windham County. — The source of Dummerston granite is a dome
about 1 square mile in area which rises approximately 900 feet above
West River, about 5}4 miles from Brattleboro. Sheeting planes 6 inches
to 2 feet apart, in a zone 25 to 35 feet thick with much more widely spaced
sheeting planes both above and below, are an unusual feature. Major
joints strike N.15°E. and are 7 to 30 feet apart. Rift and grain are
pronounced, the former being vertical, with a N.15°E. course, and the
latter horizontal. There are two main types of granite, the better
known being the "Dummerston White," an even-grained, light gray
rock speckled with bronze mica, which is used for building, monuments,
paving stones, and curbing; the second type is a light bluish gray rock
employed for monuments.

Windsor County. — The best known Windsor County granite is
quarried at Bethel, on Christian Hill, a dome at least one half mile long,
550 to 650 feet wide, and 350 feet high. The rock is a bluish or milk-
white muscovite granite, of medium to coarse texture. Sheeting planes
are 6 inches to 8 feet apart. Major joints are variable but follow a
general east-west direction. The rift is horizontal or dips eastward
slightly, and the grain is vertical, with a nearly east-west course in the
largest quarry. "Bethel White" is used for both monumental and build-
ing purposes but is particularly adapted for the latter. The Union
Station and the Post Office at Washington, D. C, were made of this stone.
It is one of the whitest granites quarried and is often mistaken for marble.

A light greenish gray muscovite granite, well-adapted for building,
occurs near Rochester. "Plymouth White," "Windsor Granite," and
"Ascutney Green" are commercial types found near Plymouth and
Windsor.

Massachusetts. — Massachusetts ranked second as a producer of
dimension granite, with an output in 1928 valued at $3,749,668, or 15.2
per cent of the total for the United States. Corresponding figures for

GRANITE 117

1929 are $4,005,083; for 1930, 3,024,669; for 1936, $2,003,302; and for
1937, $1,956,408. Unlike Vermont producers, who specialize almost
exclusively in monumental stone, Massachusetts quarrymen diversify
their production. Of the 1928 production 45.5 per cent was building
stone, 24 per cent monumental, 10.2 per cent paving stones, 18.9 per cent
curbing, and 1.4 per cent rubble. During recent years a gradual increase
in the proportion of building stone has been noted. There are several
important producing centers, notably Quincy, Milford, West Chelmsford,
and Rockport, as well as quite a number of less productive areas scattered
throughout the State.

Berkshire County. — The more important granites of Berkshire County
occur near Becket. The rock is a fine-grained, bluish gray muscovite-
biotite granite with a tendency toward gneissic structure. Two main
types are marketed as memorial stones, "Chester dark" and "Chester
light," the variation in color being due to differences in the proportion
of biotite present. Sheeting planes are 6 inches to 30 feet apart and
thicken gradually with depth. Joints are in two prominent systems,
which intersect at right angles. Gray granite has been quarried at Otis.

Bristol County. — Important deposits of rock in two colors occur near
Fall River in southeastern Massachusetts. "Fall River Pink" is a
pinkish gray, gneissoid, biotite granite; "Fall River Gray" is similar,
except that it is light buff-gray. Both are suitable for rough, massive
construction and for curbing. Sheets are 13^^ to 16 feet thick, and joints
are spaced 20 to 200 feet apart. Pegmatite, aplite, and basic dikes occur
in places, and black knots in the form of inclusions are not uncommon.

About 2 miles northwest of New Bedford is a deposit of substantial
and attractive building granite. The "New Bedford" is a light pinkish
gray biotite-muscovite granite gneiss of coarse texture, cut by an unusual
series of dikes, including diorite, diabase, and pegmatite. Rough and
dressed building stone, paving blocks, and curbing are the chief products.

"Dartmouth" granite is quarried about 8 miles southeast of Fall
River. It is similar to the New Bedford stone, except that it is light
buff-gray. The sheets are 1 to 12 feet thick, the rift is horizontal, and
the grain is vertical. It is used for rough construction and curbing.

Essex County. — An olive-green hornbende-augite granite somewhat
resembling that quarried at Quincy is found in the Peabody-Lynnfield
district, southern Essex County. The rock, known to the trade as
"Peabody Green," is used for trimming, base courses, steps, curbing, and
paving stones.

The most important granites of the county occur on Cape Ann, at
the extreme east. The entire cape is made up of granites and related
rocks, though they are covered in part with sandy hillocks, flats, and
marshes. Rockport granite is of two main sorts — gray and green. The
grays are abundant and are known commercially as "Rockport Light

118 THE STONE INDUSTRIES

Gray," and " Bayview Gray." The latter is a medium- to coarse-grained,
black-spotted gray hornblende granite which is rather hard to work
because of a high content of free quartz. The second type, known as
"Green Granite" or "Seagreen," is a dark, black-spotted, olive-green
hornblende granite. As already stated, a conspicuous feature of the
Rockport quarries is the large number of basic dikes which traverse
them. Pegmatite dikes and black knots are not uncommon. The rift is
generally east-west and vertical, and the grain horizontal. Sheets are
6 inches to 35 feet thick. Numerous joints intersect at various acute
angles. The rock is adapted to a variety of uses. As the location of
the quarries at tidewater is a great advantage for shipping many large
blocks are quarried for docks and other types of heavy shore-line con-
struction. The granite is also used for rough and dressed building stone,
rough and dressed monumental stone, paving blocks, curbing, and rubble.
The two large fountains on the Union Station plaza, Washington, D. C,
are made of the sea-green stone.

Hampden and Hampshire Counties. — A fine-grained, dark gray,
quartz-diorite gneiss found near Monson is used chiefly for building and
curbing. The banding is attributed to flow structure rather than to
metamorphism. A gneissoid granite similar to the Monson, quarried in
a small way at Pelham, has been used principally for local building.

Middlesex County. — A light bluish gray biotite-muscovite granite
gneiss (more properly a quartz monzonite), quarried near Acton, is used
chiefly for building and curbing. Coarser grained granites from the
vicinity of Groton are used chiefly for paving stones.

Important deposits occur near Graniteville, Westford, West Chelms-
ford, and Lowell. The ''Oakhill," from the neighborhood of Westford,
is a light bluish gray muscovite-biotite granite gneiss. It is medium-
grained and slightly porphyritic. Sheets are 8 inches to 12 feet thick.
Joints are in three main systems intersecting at oblique angles. The
rift is horizontal and the grain vertical. The best-quality rock is used
for monuments and dressed building stone, and the coarser and less
uniform material for bridges, rough building stone, paving blocks,
curbing, and rubble. The ''Graniteville" is similar, though generally
lighter in color. About a dozen companies, some with extensive quarries,
operate in the West Chelmsford- Westford district. The largest quarry
at West Chelmsford is about 1,500 feet long, 500 feet wide, and 100 feet
or more deep. Sheeting planes are horizontal, and sheets are progres-
sively thicker at depth. Vertical joints are widely spaced. The quarry
is exceptionally well-equipped for production of building stone, curbing,
and paving stones.

Norfolk County. — The granite industry in the neighborhood of
Quincy is one of the most important in the United States. The rock
occurs 7 or 8 miles south of Boston in the Blue HiUs, a ridge which attains

GRANITE 119

a maximum height of about 640 feet. The quarries are in a lenticular
area about 10 miles long from east to west, and one half to 2 miles wide.
The rock is of unusual composition, being described as a riebeckite-
aegirite granite. Riebeckite and aegirite are varieties of amphibole and
of pyroxene, respectively, both rich in soda and iron but low in alumina,
magnesia, and lime. Average Quincy granite consists of about 60
per cent feldspars, 31 per cent quartz, and 9 per cent riebeckite and
aegirite. Unlike most granites it contains no mica. In color it ranges
from medium or greenish gray to dark bluish gray. The bluish shades
probably are due to the presence of the riebeckite and the greenish color
to the aegirite. It is a medium- to coarse-grained rock of uniform texture
and is noted for its ability to take a high polish. The darker varieties
are marketed, chiefly as rough monumental stone, to manufacturers who
distribute it to retail monument dealers in all parts of the country.
The various trade names are "Quincy Medium," "Quincy Dark,"
"Quincy Extra Dark," and "Goldleaf." The last is the lightest shade
of monumental stone sold, and is characterized by yellowish and reddish
specks of iron oxide derived in part from oxidation of the unusual mineral,
aenigmatite. "Extra Light" or "Pea-Green" are even lighter colored
varieties, used principally for building.

Sheet structure is well-defined in places, the planes ranging in spacing
from 6 inches to 27 feet. The sheets consist of lenses with an undulating
course, usually parallel to the rock surface, and with increasing thickness
at depth. Planes have been found at a depth of 250 feet. In other
parts of the deposit the sheeting is obscure and irregular. Joints are in
several systems, meeting at various oblique angles. As their course is
followed downward many disappear, and new ones may appear at various
levels. Such discontinuity is characteristic of the Quincy district.
The spacing of joints is very irregular, ranging from 1 or 2 to over 100
feet. Another unusual feature is the presence of rift and grain, both in
vertical directions. Generally the course of the rift is from N.65°W.
to west, and the grain is about north and south, though there are excep-
tions. Frequently the grain is obscure. Trap dikes and black knots
occur in places.

The Quincy granite industry first became important in 1825, when
stone for Bunker Hill monument was quarried. For many years five to
eight companies have been in operation, and the annual value of their
combined product has been $370,000 to $675,000.

Granite is produced in several places in Norfolk County outside the
Quincy district. In the extreme east, near Cohasset, a mottled yellowish
gray granite of coarse texture is quarried for monuments and church
interiors.

At Weymouth, south of Quincy, a gray granite is sold for decorative
ashlar and rough masonry. The walls of the closely spaced joints are

120 THE STONE INDUSTRIES

stained yellow and brown, providing variegated colors for seam-faced
stone now so popular with architects. A coarse-grained gray stone
quarried near Stoughton is used for local building. A light gray, medium-
grained hornblende granite from Wrentham is used for building and
curbstones.

Plymouth County. — At Hingham, in the northeastern part of the
county, a greenish gray aplite is quarried for building purposes. Few
sheeting planes occur, but joints are numerous and closely spaced. As
the rock is stained to a rusty color in the numerous seams it is not suitable
for monumental work but fulfills modern demands for decorative building
admirably. Like the rock near Weymouth, described in the preceding
paragraph, it is marketed as seam-faced granite and has been used in
many notable buildings. Stone for similar uses is obtained near Lake-
ville in the southern part of the county.

Worcester County. — The most important granite district of Worcester
County is near Milford, about 16 miles southeast of Worcester. Between
15 and 20 quarries have been opened in various parts of this extensive
deposit. The Milford rock is a light pinkish or greenish gray biotite
granite characterized by black spots of mica. It is of medium to coarse
texture, with a slight tendency toward banding or parallelism which is
attributed to flow structure. When the rock is cut parallel with the flow
structure the black spots are largest, because the mica flakes parallel
this direction. Another characteristic feature is the blue color of the
quartz grains. The rock is cut by diorite, aplite, and porphyritic granite
dikes. Black knots are present in places, some being inclusions and some
segregations. Sheeting planes are 6 inches to 18 feet apart. Joints are
in three main systems N.10°E., N.45°-60°E., and N.55°-70°W.; though
they are also found in other directions. The rift is uniformly horizontal
and the grain vertical, ranging in direction from N.40°E. to east-west.
''Milford Pink," the prevailing commercial type, has a pleasing color,
either with tool-dressed or polished surface, and is particularly effective
for carved or other architectural work. It has been used in many large
buildings in the Eastern and Middle Western States, notably in the
Pennsylvania Railroad station in New York.

At Uxbridge, about 8 miles southwest of Milford, a light gray,
medium-textured biotite granite gneiss, useful for construction purposes,
is quarried. Though sheets are absent, joints are numerous. Alteration
or staining from the joint surfaces forms the so-called "sap" rock to a
depth of a foot in places. The stone is used for rough construction,
dressed building stone, curbing, and rubble and to some extent for
monuments.

Near Fitchburg in the northern part of the county a light bluish gray
muscovite-biotite granite gneiss is quarried for building stone, paving
blocks, and curbing. A little rough construction stone is obtained at
Holden, near Worcester.

GRANITE 121

Minnesota. — Minnesota, which ranked third in production, has
deposits of high-grade granites of several distinctive types. The major
part of the industry is centered near St. Cloud, in Stearns and Sherburne
Counties, about 60 miles northwest of Minneapolis. St. Cloud ranks
second as a national monumental granite center, being exceeded in value
of output only by Barre, Vt.

The value of dimension granite produced in Minnesota in 1928 was
$2,637,704, or 10.6 per cent of the total for the United States. Corre-
sponding figures for 1929 are $3,226,665; for 1930, $2,648,909; for 1936,
$1,205,688; and for 1937, $883,179. Building-granite production is a
much more important industry in Minnesota than in Vermont, as about
40 per cent of the output is used for construction and 60 per cent for
monumental purposes. Paving-block and curbing production have
become almost negligible in recent years.

Minnesota granites occur in two main districts. Those usually classed
as of lower Keweenawan age outcrop in many parts of central Minnesota,
notably in Stearns, Sherburne, Benton, Morrison, and Millelacs Counties;
in the southwestern part of the State, along the Minnesota River Valley
from New Ulm to Ortonville, those of Archean age occur. Granites
appear in other counties but are not considered here, as they are utilized
to a very limited extent as dimension stone. Recently a small production
of monumental and rough building stone has been reported from St.
Louis County in the far north.

As the granites occur in two distinct areas it seems more logical to
consider each separately than to discuss the occurrences alphabetically
by counties.

St. Cloud District. — Granites occur at or near the surface over an area
of about 200 square miles near St. Cloud, "the Granite City." The
most active quarry region, in which 25 to 30 companies operate, is 3 to 4
miles west and southwest of the city. Many well-equipped mills for
cutting and polishing are situated in St. Cloud; and, unlike those of the
Barre district of Vermont, most of the mills are operated by quarry
owners. Therefore Minnesota products enter the market as cut or
dressed stone, whereas much of the Vermont production is sold in rough
blocks. On this account, the unit value of the Minnesota stone is much
higher than that of the Vermont product.

The rock is of three main types, "St. Cloud Red," "St. Cloud Gray,"
and "Rockville." The red granite is medium- to coarse-grained, the
feldspars averaging about one fourth inch in diameter. These minerals,
which constitute about 75 per cent of the rock, consist of orthoclase and
microcline with a smaller amount of plagioclase. Quartz, forming about
15 to 20 per cent of the rock, occurs in coarse glassy grains. Hornblende
and biotite form 5 to 10 per cent. The rock is deep red, is very attractive
when polished, and is therefore used chiefly for monuments. The gray
granite consists principally of orthoclase, plagioclase, hornblende, and

122 THE STONE INDUSTRIES

quartz, the last mineral being much less prominent than in the red
granite. It is used chiefly for monuments, though a subordinate amount
is used for paving blocks and curbing. "Rockville" is much coarser-
grained than the red and gray types, the feldspars being one half to three
fourths inch across. It is a pinkish gray biotite granite, consisting of
feldspar, chiefly orthoclase, quartz in large glassy grains, and black mica.
Though used for monuments to some extent, it is essentially a building
granite.

The deposits are cut by granite, aplite, and trap dikes. In many
places red granite dikes cut the gray, while the converse is never found,
indicating that the red granite is a later intrusion. Aplite dikes are
common, especially in the gray granites. Diabase or trap dikes, occurring
in many places throughout the region, range in width from a fraction of an
inch to 6 or 8 feet. Hair lines of various types are present. Black
knots, both segregations and inclusions, are not abundant but are fre-
quent enough to be troublesome. As stated earlier, joints are well-
developed, usually in two major systems, one running approximately
north and south and the other east and west. They are spaced at
convenient intervals for quarrying, usually 2 to 12 feet apart. Sheeting
planes are scarce or entirely absent, a circumstance which makes quarry-
ing difficult. The rift is horizontal and the run vertical, ordinarily
north and south.

Stearns County. — The chief quarry district is in western St. Cloud
township, where 15 to 20 quarries are in operation. Both red and
gray granites are quarried. The rock occurs in a series of low domes
which may be worked as shelf quarries of shallow depth, but most of the
quarries are deep enough to be of the pit type. The rift and run are more
pronounced in the gray than in the red, on which account the former is
better adapted for paving stones and curbing. For monumental uses
the deep reds are more desirable. Quarrymen have their own special
trade names, among which may be mentioned "Rose Red St. Cloud,"
''Indian Red St. Cloud," "Victory Red St. Cloud," "St. Cloud Superior
Red," "Red Rock," "Melrose Red," "Minnesota Mahogany," "Black
Diamond Red," "Red Pearl," "North Star Red," "St. Cloud Gray,"
"Victory Gray St. Cloud," "St. Cloud Superior Gray," "Melrose
Gray," "Pioneer Gray," "Royal Gray," and "Dark Gray." The
granites are much in demand and are widely marketed, even in States far
from the quarries.

The Rockville district is about 10 miles southwest of St. Cloud in a
pale pink coarse-grained granite of exceptionally uniform texture and
color. The rock rises in a dome which is exposed over at least an acre.
Open joints are far apart and somewhat irregular in direction. The most
prominent strike N.70°W. ; others strike N.45°E., N.55°W., and N.10°W.
If joints were closely spaced, this irregularity would result in much

GRANITE 123

waste rock, but here where they are spaced 20, 40, and even 100 feet apart
the irregularity has httle consequence. In fact, quarrying would be
much easier if they were spaced more closely. There are also few
sheeting planes. The rock is so uniform and so free from defects that
very little waste results. "Rockville" granite is an attractive structural
stone, for the cleavages of the coarsely crystallized feldspars give a
glittering reflection on the hammered surface. It is also well-suited for
carving, but is used to a limited extent for monuments. The granite is
quarried by two long-established companies and is sold under the trade
names ''Minnesota Pink" and "Minnesota Pearl Pink." It has been
used in many notable buildings, for example, in the cathedral at St. Paul,
Minn.

Sherburne County. — Granites are available only in the northwest
corner of Sherburne County. Though red and some intermediate
varieties are present, gray predominates. The gray rock has a horizontal
rift and vertical run (grain) north and south. Black knots and aplite
dikes occur in places. Most of the joints are widely spaced. In some
quarries sheeting planes are 4 to 16 feet apart; in others few are encount-
ered. The rock is adapted chiefly for building and for paving blocks.
One large quarry is operated by the State reformatory, and the rock is
used for construction of the main building and walls. Several companies
operate in both red and gray granite, producing building stone, paving
blocks, curbing, and monument stock. During recent years, however,
paving and curbing manufacture have decreased greatly. "Minnesota
White" and "Hilder Gray" are common trade names.

Benton County. — Outcrops are more numerous in Benton than in
Sherburne County, but the rocks are less uniform and present a greater
diversity of types. The most abundant rock is a dark diorite some of
which has been used for building stone, paving blocks, and monumental
stock.

Mille Lacs County. — On the west branch of Rum River a few miles
west of Milaca a red granite is quarried for monuments and sold under
the name "Sunset Red." Most of the rocks in the county are diorites
and are not attractive for high-grade work.

Morrison County. — A granite of the "St. Cloud Red" type is quarried
near Glenola for manufacture of monuments. A dark, fine-grained rock
quarried near Little Falls is described as an augite-diorite, consisting of
numerous lathlike crystals of plagioclase, biotite, green hornblende, and
almost colorless augite. It is marketed as a black granite under the trade
name "Little Falls Black."

The Granites of the Minnesota River Valley. — Thousands of years ago
an immense volume of water derived from melting ice sheets and from
rainfall over an area that may almost be termed continental poured down
the valley of what is now the Minnesota River. In its passage it swept

124 THE STONE INDUSTRIES

away all decayed and weathered debris and eroded a valley 2 miles wide in
places, a valley entirely out of proportion in magnitude to the small
river that now flows through it. Ancient Archean rocks ordinarily
protected by a covering of Cretaceous sediments, are exposed in this
valley; and not only have overlying formations been removed, but the
scouring effect of the great river has swept away the upper zone of
weathered granite, leaving the rock fresh and unaltered at the surface.
Both granite and granite gneiss outcrop in many places, and have been
quarried at various points between Odessa and Morton.

Big Stone County. — There are numerous outcrops near Ortonville,
Odessa, and Correll. The " Ortonville " stone is a deep red biotite granite
or granite gneiss, which takes an excellent polish. In quarrying, much
waste results from the presence of pegmatite dikes, black knots, and
closely spaced or irregular joints. Monumental stone and ornamental
columns sold as "Ruby Red" have been obtained from these deposits.

Redwood and Renville Counties. — The best rock in these counties occurs
in outlying masses in the Minnesota River Valley. These are prominent
domes at North Redwood and across the river from Morton; near the
latter town a dome covers many acres and reaches an elevation which
affords an extensive view of the river basin from its summit. The rock
exhibits little or no weathering, even at the surface. Two types are
available near North Redwood — one a medium-grained, greenish gray
biotite gneiss, and the other a pale pink biotite granite or quartz diorite.
Both rocks are even-grained and are exceptionally attractive for monu-
mental and building uses. A type known as "Rainbow" granite is well
known in the monument trade.

The rock near Morton is a biotite granite gneiss with distinct banding.
Although of uneven texture it takes a good polish, and about half of the
production is suitable for monumental stone. It is also used for monu-
ment bases, curbing, building stone, and bridge construction. It is
very strong, even in a direction parallel to the banding. Sheeting planes
are 12 to 20 feet apart and dip 5 to 15°, always toward the margin of the
dome. Major joints are 6 to 30 feet apart, in systems approximately at
right angles. Black knots and streaks are present in places. The
strength of the rock and its availability in large sound blocks make it
particularly suitable for heavy construction.

North Carolina. — The value of block granite produced in North
Carohna in 1928 was $2,253,435, or 9.1 per cent of the total for the
United States. As in Massachusetts, the production is diversified; 43.7
per cent of the total for the year was building stone, 15 per cent monu-
mental stone, 13.7 per cent paving blocks, 26.2 per cent curbing, and 1.4
per cent rubble. Building granite has become increasingly important
in North Carolina since 1926, the growth in volume being due to the
increased use of ashlar granite in medium-priced dwellings. So much of

GRANITE 125

the production was "undistributed" in the years 1929 to 1937 that
figures obtainable do not give a true picture of the extent of the industry.

Granites and gneisses are distributed widely in the State, being found
in all three of the larger geologic provinces— the Coastal Plain, the
Piedmont Plateau, and the Appalachian Mountains. Those that have
been used most are in the Piedmont Plateau region.

Granites occur in several counties of the Coastal Plain in the region
bordering the Piedmont Plateau, and are extensions of the crystalline
rocks of the latter region beneath the Coastal Plain sediments. They
range from fine even granular to coarse porphyritic in texture and from
gray to pink in color. Most of them are biotite granites. Joints
are well-developed in three main systems, northwest, north, and
northeast. Diabase dikes are of common occurrence.

Much stone of good quality is readily available within the limits of
the Piedmont Plateau. Numerous quarries have been worked over
many parts of this region, which has been divided geologically into four
belts. The northeastern area, including Wake, Franklin, Vance, Gran-
ville, and Warren Counties, borders the Coastal Plain. Most of the
granites in this section are schistose and therefore have limited commercial
value. In certain areas, however, granites of good quality for building
purposes have been worked for many years. The next belt to the west
consists of slates, schists, and altered volcanic rocks, with little or no
granite of commercial value. West of this is the central belt, including
Mecklenberg, Gaston, Cabarrus, Iredell, Rowan, Davidson, Davie,
Forsyth, Guilford, and Alamance Counties, where biotite granite is one of
the principal and most widespread rocks. It occurs in each of the 10
counties mentioned and has been quarried from time to time, usually to
satisfy local demands. Two distinct types occur, an even granular rock
and a porphyritic granite, much of which shows evidence of gneissic or
schistose structure. Colors range from white to various shades of gray
and occasionally pink. The western belt includes Surry, Wilkes, Alle-
ghany, Alexander, and Cleveland Counties, with greatest development in
Surry County. This area is well-supplied with railway lines, which
greatly aid marketing. The commercial granites here are in the form of
igneous intrusions of both massive and schistose types.

The Appalachian belt is mountainous, and quarrying has been
confined chiefly to a few areas of gneiss suitable only for crushing or for
rough construction. In Madison County an area of mixed dark green
and yellow biotite-epidote granite should prove of economic value.

The commercial granites will be considered in the three geologic
provinces in succession:

Coastal Plain Granites, wilson county. — Only small areas of granite
are exposed in Wilson County, the more important about 3 miles north
and 3 miles south and southwest of the town of Wilson. During recent

126 THE STONE INDUSTRIES

years the latter area, with exposures on both sides of Contentnea Creek, is
the only one quarried. The rock is coarse-grained, pinkish red and of
porphyritic texture. It is used for bridge construction and rough
building.

While granites occur in other Coastal Plain counties little or no
block granite has been produced in late years.

Piedmont Plateau Granites. — surry county. — The most important
granite district of North Carolina is near Mount Airy in Surry County
near the northern boundary of the State, Originally the outcrop was a
dome rising about 125 feet above the valley, but much of the upper part
has been removed. The surface area, now exposed partly as a natural
outcrop and partly by stripping, covers about 70 acres. The rock is a
very light gray, almost white, biotite granite of medium texture. The
biotite is unequally distributed; some masses contain little or none, in
consequence of which they are exceptionally white. For the most part,
however, the rock is of uniform color and texture. Veins and dikes, so
common in most granites, are nowhere evident in the Mount Airy deposit.
Absence of joints and sheeting planes is the most remarkable feature,
the rock being massive throughout, with no natural partings. It has a
horizontal or slightly dipping rift and a vertical grain — structural
features of the utmost importance in quarrying and manufacture.

Production has grown steadily since 1890, when the rock was first
quarried. Operations are now more extensive than in any other district
south of New England. The rock has exceptional merit for building
purposes and for mausoleums, as it is light in color and pleasing in
appearance, and also for bridge work, as sound blocks of any desired size
are obtainable. Granite from this deposit valued at $1,500,000 was used
in the Arlington Memorial Bridge over the Potomac River at Washington,
D, C, shown in the frontispiece. It has been employed in many large
structures throughout a wide market area extending to Philadelphia,
New York, and more distant cities. Although the chief market is for
cut stone used in bridges, dry docks, and large buildings, quite an exten-
sive market has been developed recently for the smaller fragments in the
form of ashlar for constructing moderate priced dwellings. Such material
is being shipped as far north as eastern Pennsylvania. Mount Airy
granite is also well-adapted for the manufacture of paving stones and
curbing, and the latter use accounts for about one fourth of the total
production value. It is less suitable for monuments, as the color contrast
between cut and polished surfaces is not decided enough. Both quarries
and mills at Mount Airy are equipped with the most modern machines
and appliances,

ROWAN COUNTY. — Next in importance to the Mount Airy granite are
those found near Salisbury, Rowan County. The rock rises in a nearly
continuous ridge, beginning about 4 miles east of Salisbury and extending

GRANITE 127

southward more than 12 miles. In the northern part two distinct types
occur, a very Hght gray or nearly white rock, and a pink or flesh-colored
granite. They are of identical texture and mineral content and evidently
parts of the same intrusion. In the pink rock quarried near Granite
joints are in two systems striking N.10°E. and N.70°W., and are spaced
widely enough to permit quarrying large blocks. Sheeting planes are 2
to 8 feet apart. The rock is notably free from veins or dikes, is medium-
grained, uniform in texture, and attractive in color. It is sold both rough
and dressed and is popular as a monumental stone marketed under the
trade name "Balfour Pink."

In the gray rock, also quarried near Granite, joints are less systematic
than in the red but are widely spaced. The stone has good working
qualities and dresses well under the hammer. It has been used widely
as a building stone and for curbing and paving but little for monuments.
Similar granites, both gray and pink, are quarried near Faith, 5 to 9 miles
south and southwest of Salisbury.

DAVIDSON AND WAKE COUNTIES. — Gray granites of various types occur
in Davidson County, but in recent years they have been quarried only in
the vicinity of Southmount and used chiefly for paving blocks. In the
vicinity of Wake Forest in the northern part of Wake County a medium-
to fine-grained, light gray biotite-muscovite granite is quarried for build-
ing, curbing, paving blocks, and rubble.

Appalachian Mountain Granites. Henderson county. — A medium-
grained, light gray biotite gneiss occurs near Hendersonville, It is of
uniform color and texture, though a few black knots occur in places.
Large blocks are obtainable. Most of the granite quarried in Henderson
and in Buncombe County to the north is used for crushing, though it is
used to some extent in rough construction.

Maine. — The value of granite in the form of dimension stone produced
in Maine in 1928 was $2,249,715 or 9.1 per cent of the total for the
United States. Paving stones, which represented 54.8 per cent of this
amount, are the chief products. Maine produced more than 42 per cent
of all the granite paving blocks in the country. The value of building
stone was 25.2 per cent, monumental stone 6.9 per cent, curbing 12.9
per cent, and rubble 0.2 per cent of the total. There is evidence of a
trend toward a larger percentage of building-granite production, as the
location of quarries at the coast is favorable for water transportation to
New York and other coast cities, where it is gaining in popularity.
Production in 1929 was valued at $2,630,266; in 1930, $2,039,058; in 1936
$1,212,855; and in 1937, $1,280,122.

Granite is distributed widely in Maine ; in fact, it is the most abundant
rock. It occurs in three main areas — in the western tier of counties,
along the eastern coast, and in the Mount Katahdin area in the north-
central part. In addition, there are three small areas in Lincoln, Ken-

128 THE STONE INDUSTRIES

nebec, and Somerset Counties. Except for important centers at Hallowell,
Kennebec County, North Jay, Franklin County, and several develop-
ments of minor importance, all quarries are along the seaboard, either on
or within a few miles of navigable waters. The industry is centered in
Penobscot and Bluehill Bays and the islands in or adjacent to them.
Occurrences now of commercial importance will be described by counties
in alphabetical order,

Cumberland County. — A fine, even-grained gray biotite granite is
quarried about 33^^ miles northeast of Westbrook. It has a distinct flow
structure which gives it the appearance of a gneiss. Sheeting planes are
6 inches to 2}^ feet apart and nearly horizontal. Joints are few, and the
rift is horizontal and grain vertical, striking eastward. The rock is used
for monuments and curbing.

Franklin County. — An important granite center of the county, par-
ticularly for building granite, is at North Jay. The rock, a light gray
biotite-muscovite granite of fine, even-grained texture, is known to the
trade as "North Jay White." The whiteness is due to the quartz being
clear, not smoky as in many granites, and to the light color of the feldspars
visible through the quartz, as well as on the surface. The sheets are 4
inches to 6 feet thick, being quite thin in the upper 25 feet and gradually
thickening at increasing depths. The chief joints run N.62°E., N.70°E.,
and N.50°W. and are widely spaced. The rift is horizontal, and there is
no grain. Black knots are rare, but a few pegmatite dikes are present.
The rock is exceptionally attractive for building, though it is also used
extensively for monuments, mausoleums, paving stones, and curbing.
Though one of the few important granite centers of Maine distant from
tidewater, it has direct rail connection, and its products are widely
employed not only in New York, Philadelphia, and other eastern cities
but also throughout the Middle West.

Hancock County. — More granite is produced in Hancock than in any
other county in Maine. Over a dozen quarry companies operate near
Franklin. The rock is a medium- to coarse-grained, gray biotite granite,
of uniform texture. Sheeting planes are 2 to 13 feet apart. For the
most part, joints are widely spaced. The rift is horizontal and grain
vertical, usually striking east-west. Black knots and trap dikes are not
unusual. Paving blocks, curbing, and monument bases are the chief
products.

A light buff to gray biotite granite of medium to coarse, even-grained
texture is quarried near Mount Desert. The four chief minerals — buff
orthoclase, milk-white plagioclase, smoky quartz, and black biotite —
present very attractive color contrasts which are enhanced by polishing.
In one part of the deposit the rock is pinkish gray and is marketed as
"Sommes Sound Pink." Sheets are 2 to 12 feet thick. Widely spaced
major joints strike N.25°W., N.50°E., and N.85°E. The rift is horizontal,

GRANITE 129

and grain vertical, usually striking east-west. Dark gray knots up to 6
inches in diameter occur in places. The quarries are close to tide-water,
and the wharves are accessible to schooners of 20-foot draft. Building
stone, monument stock, and paving stones are the chief products. The
stone has a wide market and has been used in many important structures.

Another important quarry district covers an area of about 4 square
miles around Stonington, including parts of Deer Isle and Crotch Island.
On the southern half of the latter island the rock rises in a dome about 140
feet above sea level. At its center the sheets are horizontal but dip
downward at angles of 10 to 25° toward both the northwest and the
southeast. East- west vertical joints are prominent. The Crotch Island
rock, a coarse, even-grained, gray biotite granite with lavender tint, is
well-suited for massive construction. Its polished surface shows pleasing
contrasts, and on this account it is in demand for base courses, wainscot-
ing, and monuments.

An important deposit of similar granite occurs on Deer Isle and is
quarried about 2 miles from Stonington. Sheets are 6 inches to 16 feet
thick and dip 10 to 15° north and south, away from the top of the hill.
Joints are widely spaced, the rift is vertical and runs N.60°-65°W., and
knots are rare and small, but granite dikes 4 to 12 inches thick occur in
places. The stone is used widely for massive construction, such as for
piers, sea walls, and bridges and also in many large buildings.

Near Sullivan a fine- to medium-grained, uniform gray biotite granite
is quarried. The sheets in one quarry are 3 to 8 feet thick. Joints
strike N.80°-85°W. and N.10°-20°E. There are many black knots. In
another quarry the sheets are only 1 to 5 feet thick. A coarse- to medium-
grained gray granite is also quarried in this district. Paving blocks and
curbing are the chief products. Similar granites are quarried for monu-
ment bases, paving blocks, and curbing near North Sullivan.

Kennebec County. — An important inland stone-producing district near
Hallowell is one of the oldest in the country, the quarries first having
been opened in 1826. Though a considerable distance from the coast,
they are only 2}-^ miles from a wharf on the Kennebec River and are
accessible to schooners of 12-foot draft. The well-known, fine-textured,
light gray "Hallowell granite" consists essentially of feldspar, quartz,
biotite, and muscovite. The most striking structural feature of the
quarries is the gradual increase in thickness of the sheets downward, from
4 inches to 14 feet. Joints are spaced more closely than in many New
England granites and intersect the rock at various angles. The rift is
horizontal, and a poorly developed grain vertical, striking N.25°W.
Black knots occur in places, and sap rock bordering the joint planes may
be a foot deep. The stone is widely used for building purposes, where it
is particularly adapted to carving, and also for monuments and paving
stones.

130 THE STONE INDUSTRIES

Knox County. — The principal quarries of Knox County are near
Long Cove, St. George, and South Thomaston, south and southwest of
Rockland, and on Vinalhaven Island. In the former region most of the
rock is fine- to medium-grained and blue-gray. Sheeting planes are 2 to
13 feet apart and usually dip at small angles. Joints vary in direction
and are closely spaced in places. The rift is vertical, with a general east-
west course. Many paving blocks are made and as the stone takes a
good polish it is popular also for monuments.

Vinalhaven and the adjacent islands have been known as the Fox
Islands, and their granite as " Fox Island Granite." Many quarries have
been operated at various times, chiefly near Vinalhaven Island and on
Hurricane Island. During recent years two companies have been
responsible for the chief production. Much of the rock is pinkish buff
and coarse textured, but some quarries produce a fine, even-grained, gray
granite. In this rock sheets are 1 to 6 feet thick; vertical joints strike
N.80°W. and N.5°-10°E. The rift is vertical, striking N.5°-10°E. In
the coarse rock, sheets are 2 to 10 feet thick, and the joints are in several
intersecting systems. Although building stone has been produced from
these quarries, recent production has been confined principally to paving
stones. An attractive black granite is quarried at Vinalhaven.

Lincoln County. — A fine-grained dark gray quartz diorite, classed
commercially with the "black granites," is quarried near Round Pond
for monuments and paving blocks. Sheets are 1 to 12 feet thick. Major
joints striking N.60°E. are 5 to 40 feet apart, and a second system
N.40°W. is at wider intervals. The rock is cut by both pegmatite and
trap dikes. It takes a good polish and shows marked contrast between
tooled and polished surfaces.

Somerset County. — A light gray, even-grained granite with a distinct
flow structure has been quarried at several points about 2}^ miles south
of Norridgewock. It is used for both buildings and monuments.

Waldo County. — A fine- to medium-grained, light gray, muscovite-
biotite granite is quarried near Lincolnville, chiefly for monumental use.
The sheets are 6 to 15 feet thick and dip 25°S. The chief joints strike
N.60°-65° W. The rift is vertical and parallels the major joints. Quarries
at Mt. Waldo near Frankfort, which had been idle 25 years, were reopened
in 1930 and equipped to produce building granite on a large scale. The
rock is a fine, even-grained, gray biotite granite. Stone from these
quarries was used extensively in the George Washington Bridge at New
York. Water transportation on the Penobscot River is available.

Washington County. — Washington County granites are of two main
types— ''black granites" and medium-grained pinkish gray biotite
granites. Some of the so-called black granites are norites but that
quarried near Addison is a gabbro which poHshes to a jet-black surface
mottled with a little white, and one occurring near Calais is a dark gray

GRANITE 131

quartz diorite. As they all take a good polish, they are used for monu-
ments. The pink granites, one of which is sold under the trade name
"Back Bay Pink," quarried near Marshfield and Millbridge are used for
monuments and building.

York County. — A coarse-grained, light gray granite occurs near
Biddeford in sheets 1 to 15 feet thick. The rift is vertical, and the grain
horizontal. It is used for monuments and rough construction. "North
Berwick Black Granite" (gabbro) quarried near North Berwick is well
adapted for monuments.

Georgia. — Block granite produced in Georgia in 1928 was valued at
$1,985,838, or 8 per cent of the value of total production for the United
States. About 26 per cent was sold as building stone; 21 per cent,
monumental; 19 per cent, paving blocks; 33 per cent, curbing; and 1 per
cent, rubble. Although fluctuations have occurred the trend in produc-
tion was gradually upward from the World War until 1928. Production
in 1929 was valued at $1,741,938; in 1930, $1,673,529; in 1936, $920,355;
and in 1937, $875,529.

The granites of Georgia are entirely within the limits of the Piedmont
Plateau, a northeast-southwest belt extending from the eastern base of the
Appalachian Mountains to the Coastal Plain sediments occupying the
middle-northern part of the State. Dimension stone is produced in
three main districts — in the vicinity of Stone Mountain and Lithonia in
De Kalb County, near Elberton in Elbert County, and near Sparta
in Hancock County.

De Kalb County. — The most notable occurrence of granite in Georgia
is Stone Mountain in eastern De Kalb County. It is a massive dome
measuring 7 miles in circumference at its base and rising 686 feet above
the adjacent lowlands. The rock is an even-textured, medium-grained,
light gray muscovite-biotite granite of uniform color and texture. Joints
in two well-defined systems, striking northeast and northwest are widely
spaced, as are also the sheeting planes. The granite is well-adapted for
building purposes and for bridges and mausoleums, as it is available in
sound blocks of any desired size. Paving blocks, rubble, and a limited
amount of monument stock are also produced. A wide market has been
developed for the stone in Northern and Middle Western States, as well
as in Atlanta and other adjacent cities. One large company has operated
for many years on the flank of the dome.

A project to carve in massive proportions high on the cliff face a
group of great Confederate generals has created much interest in Stone
Mountain during recent years. The actual carving was begun in June
1923, but work was suspended 3 or 4 years later with the task far from
completed.

In the Lithonia district the rock a fine-grained, highly contorted
biotite granite gneiss, occurs in similar bosslike masses, though much

132 THE STONE INDUSTRIES

smaller than Stone Mountain. Red garnet and tourmaline are present
in places, the latter mineral being associated with pegmatite dikes. In
some quarries well-defined joint planes appear, while in others they are
few in number. Sheeting planes are absent. The rock has a distinct rift
and grain which are of great assistance in quarrying. Eight or ten com-
panies have worked the deposits for many years. The chief products, pav-
ing stones and curbing, are sold in Atlanta and other southern cities and
also shipped to many distant points. Rubble is produced as a byproduct.

Elbert County. — Granite is confined chiefly to the middle southwestern
part of the county, though it extends into adjacent counties. In many
places the rock appears in bare outcrop. There are two main types — a
fine- to medium-grained, light gray, biotite granite and a dark blue-gray
granite similar to the first, except in color. The former is best adapted
for building purposes. The blue-gray granite is so uniform in texture
and attractive in color and general appearance that it is used widely as
monumental stone. Several companies operate in the district and
market their products under various trade names, such as "Elberton
Blue," "Oglesby Dark Blue," and "Oglesby Light Blue." Red or pink
granites occur less commonly. One commercial variety is sold under the
trade name "Sunset Pink." Railway facilities are available for ship-
ment to many distant markets.

Hancock County. — The Hancock County granite area is about 11
miles long and extends northeast from Sparta. The rock occurs in bare
outcrops, some several acres in extent. The prevailing type is a coarse-
grained, medium gray, porphyritic biotite granite used for curbing,
paving stones, and monuments.

Wisconsin. — The value of Wisconsin block granite produced in 1928,
as reported to the United States Bureau of Mines, was $1,581,612, or
6.4 per cent of the value of total production of the United States. Nearly
three fourths of the product in value is sold for monuments and one
fourth for paving blocks. The proportion by uses was as follows in 1928 :
Monumental stone, 72.9 per cent; paving blocks, 24.9 per cent; building
stone, 1.7 per cent; and curbing, 0.5 per cent. Production in 1929 was
valued at $1,572,010; in 1930, $1,327,913; in 1936, $673,846; and in
1937, $794,578. Paving-stone production fluctuates greatly from year
to year, with a general downward trend.

Igneous rocks underlie about one third of Wisconsin. Throughout
this area granites of many colors and textures are found, and several dis-
tinctive varieties are marketed. Dark reds and reddish browns predomi-
nate, a condition that contrasts sharply with the prevailing grays of New
England. The granites are described by counties in alphabetical order.

Ashland County. — A dark gabbro is quarried near Mellen. It takes a
good polish and is sold for monumental and building uses as "black
granite."

GRANITE " . 133

Green Lake County. — Rhyolite is quarried near Berlin, Green Lake
County. Joints and sheeting planes are numerous and intersect at
various angles, which results in the production of many small angular
blocks, though large blocks are available. The rift is nearly horizontal
and the "run" (grain) vertical. The rock polishes well on the run and
hard way but not on the rift surfaces. It is dense and compact, of uni-
form texture, and generally grayish black. "Berlin rhyolite" is strong
and durable and is used for monuments, paving blocks, and building stone.

Marathon County. — The widely known "Wausau Granite" outcrop-
ping at numerous places over an area of many square miles is quarried at
Wausau and Granite Heights. The rock now quarried is not uniform in
color but ranges from gray through reddish brown to brilliant red. Major
joints are in two systems, striking approximately northeast and north-
west. Sheeting planes are horizontal. Sound blocks of large dimensions
are obtainable in most quarries, though in some places joints are less than
4 feet apart. It is used almost exclusively for monuments and sold
under various trade names, such as "Wisconsin Mahogany," "Red
Wausau," "Wisconsin Ruby Red," and "Parcher Green."

Marinetta County. — Granite in a variety of textures and colors is
quarried along the Pike River near Amberg. Three distinct types are
produced — a fine-grained, gray granite (Pike River Gray), a coarse-
grained, red or pale pink (Amberg Red), and a coarse-grained gray. In
general the joints are spaced far enough apart to provide suitable monu-
ment stock, but in some places are undesirably close together, or intersect
at oblique angles. The rift is indistinct. In the past considerable
building stone was produced, but during recent years monument stock
is the chief product with a subordinate amount of paving stones. " Mont-
rose Red" and "Marinetta Red" are other trade names applied to the
products.

Marquette County. — High-grade granite is obtained from two mounds
near and within the city of Montello. In the larger quarry, prominent
joint systems strike N.85°E., N.25°E., and N.40°W. Many discontinu-
ous parting planes break the rock into polygonal blocks, but masses of
reasonable size for monuments are obtainable. Several greenstone dikes
(trap) follow jointing planes. Streaks or hair lines which mar some of
the rock are of two types, minute trap dikes and white quartz veins.
The rock is a dense, fine-grained granite in two colors, a cheerful bright
red and a grayish red. "Montello Granite" is a widely known, popular
monumental stone. It takes a good polish and is attractive, but is
difficult to work. Paving stones are manufactured, though not so
extensively as in former years.

Waupaca County. — A coarse-grained or porphyritic biotite-hornblende
granite of striking color and texture is quarried about 5 miles north of
Waupaca. The two more important commercial types are "Red

134 THE STONE INDUSTRIES

Waupaca" and "Gray Waupaca." The former consists of large, bright
pink feldspars surrounded by green epidote and chlorite, and the latter
is a combination of paler pink feldspars, black biotite, and hornblende.
Numerous, irregular joints cause much waste. Waupaca granite is
well-suited for interior or exterior use in monuments or buildings. On
account of its brilliant coloring it is particularly adapted for ornamental
work, such as wainscoting and balustrades.

Waushara County. — A granite deposit at Lohrville and Redgranite in
southeastern Waushara County presents favorable quarry conditions.
Major joints strike N.30°-40°W. and N.75°-80°E. and are spaced at
sufficient width to give large sound blocks. Sheeting planes 2 to 4 feet
apart near the surface provide bench floors. A decided rift strikes
N.50°E. Several coarse granite dikes traverse the deposit, and pegma-
tites, veins, and knots are present in some quarries, though in others they
are absent. About 90 per cent of the rock consists of feldspar and
quartz, with subordinate hornblende and muscovite. It is light pink
(considerably lighter than the Montello granite), is of uniform, fine-
grained texture, and takes a good polish. Three or four companies
produce monuments, paving blocks, curbing, rubble, and rough construc-
tion stone.

New Hampshire. — In 1928 the block granite produced in New
Hampshire was valued at $1,359,229, or 5.5 per cent of the value of total
production in the United States. Distribution among the various uses in
1928 on the basis of value was as follows: Building, about 50 per cent;
monumental, 19; curbing, 19; paving, 11; and rubble, 1. During recent
years building stone has shown an upward trend in production, while
that used for monuments has declined. Production in 1929 was valued
at $1,063,112; in 1930, $1,411,084; in 1936, $293,540; and in 1937,
$359,451. Granite production is confined chiefly to Carrol County in
the east-central part of the State and to Cheshire, Hillsborough, and
Merrimack Counties in the south. Gray, bluish gray, and various pinks
are the prevailing colors.

Carroll County. — Building and memorial granites are produced near
Redstone and Conway. There are two principal varieties — a coarse-
grained, light pinkish gray biotite granite, "Conway Pink," and a coarse-
grained, dark yellowish green biotite-hornblende granite, "Redstone
Green." Though in contact, they represent originally different materials.
Sheeting planes in the pink granite are 4 to 30 feet apart and arch across
the axis of the hill. The most abundant joints strike east and west and
are 5 to 40 feet apart. The rift is horizontal and the grain vertical in an
east-west direction ; they appear to follow sheets of microscopic cavities in
the quartz grains. Pegmatites and black knots appear in places. In the
green-granite quarry sheets are 11 inches to 14 feet thick and dip about

GRANITE 135

15°W. Joints, rift, and grain are the same as in the pink rock. Both
varieties are used in buildings, as well as for polished columns and
memorials.

Cheshire County. — A fine-grained, light bluish gray biotite-muscovite
granite occurs near Fitzwilliam and Marlboro, adjacent to the southern
border of the State. Estimated mineral percentages are: Quartz, about
44; feldspar, 46; and mica, 10. The granite takes a good polish and is
well-adapted for fine carving. The rift is horizontal and the grain vertical,
striking nearly east-west. In places pegmatite dikes and black knots
are present. Near Marlboro the sheets are 6 inches to 6 feet thick, and
joints are more plentiful than in the rock near Fitzwilliam, where neither
sheets nor joints are well-developed. Stone from the latter district, sold
under the trade names "Victoria White" and "Snowflake," is used for
buildings and monuments. Paving stones are the principal products of
the Marlboro quarries.

Hillsborough County. — Milford, where 10 or 12 companies are in
operation, is the most important granite center of New Hampshire.
"Milford Granite" is generally a fine, even-grained, gray rock of light
and dark shades, some having a slight bluish, pinkish, or buff tinge.
Although variable the major joints fall in a general way within two main
quadrants, N.15°-50°E. and N.35°-80°W. In some quarries they are
spaced only 3 to 5 feet apart but usually exceed 10 feet. The rift is
generally horizontal and grain vertical, striking N.70°-80°W. In places
trap dikes have altered the color of the granite. The stone takes a
good polish, with marked contrast between cut and polished surfaces;
it is also well-adapted for carving. Building stone, monuments, paving
blocks, and curbing are manufactured. A fine-grained, buff-gray monu-
mental granite closely related to the Milford rock is obtained near
Brookline and South Brookline, that from the latter locality being
marketed as "Brookline Blue."

Merrimack County. — An important deposit of fine-grained, medium
gray muscovite-biotite granite occurs on Rattlesnake Hill near Concord.
"Concord Granite" is used for cut building stone, monuments, paving,
curbing, and ashlar. In one large opening typical of the district sheets
are only 6 inches thick in the upper 30 feet but increase to a thickness of
40 feet at a depth of 130 feet. The joints, which strike N.62°E. and
N.45°W., are few. The rift is horizontal and grain vertical, striking east-
west. A few pegmatite dikes and quartz veins occur. Concord granite
was used in construction of the massive edifice of the First Church of
Christ, Scientist, in Boston, Mass. At Suncook, south of Concord, an
even-grained, light gray granite, marketed as "Allenstown Granite,"
is used for building purposes, paving blocks, and curbing. It has been
employed in many large buildings.

136 THE STONE INDUSTRIES

Minor Producing States

In preceding pages granites of the eight principal producing States
have been described. Consideration will now be given to a group of eight
States of less importance in this industry. Like the major producers,
they will be considered in the order of their production in 1928.

New York. — The value of block granite sold in New York in 1928 was
$948,991, which was 3.8 per cent of the total value of production for the
United States. About 82 per cent was used for building purposes and
18 per cent for monuments. Since 1923 the building-granite industry of
the State has grown rapidly, annual production value increasing from
less than $50,000 to nearly $800,000. This increase is due partly to the
demand for stone in the construction of the Cathedral of St. John the
Divine in the city of New York; however the demand for building granite
has decreased since 1928. Total production in 1929 was valued at only
$301,486; in 1930, $497,576; in 1931, $430,042; and in 1932, $78,661.

Production in New York is restricted to two areas, the Adirondack
region in the north and the Highlands in the southeast.

Adirondack Granites. — The most important northern granite occurs
near Ausable Forks, Clinton County. Anorthosites (granitoid rocks, the
essential mineral of which is plagioclase), syenites, and true granites occur
in this district. Although the anorthosites and granites are very attrac-
tive, recent development has been confined chiefly to the green syenites.
The typical syenite consists of about 75 per cent feldspars and 25 per
cent other minerals, including pyroxene, magnetite, and zircon. It is
medium-grained, is dark to yellowish green, takes a good polish, is
attractive for monumental purposes, and is also used to some extent for
building.

Attractive red granite is quarried on Wellesley and near-by islands in
the Thousand Island district, Jefferson County. It is suitable for
monuments and building purposes, but production has recently been
confined to paving blocks only. A gray to pinkish type occurring near
Alexandria Bay is also used in this way.

Granites of Southeastern New York. — The granite industry of West-
chester County is becoming increasingly important. Stones of two
types, light pinkish gray and a rich yellowish brown, are obtained from
the Mohegan quarry about 3 miles east of Peekskill. The yellowish
brown, one of the most attractive eastern granites for structural and
monumental work, is widely used in New York City. Joint systems and
other quarry conditions are favorable. Granite quarried about 1 mile to
the south in the Millstone Hill district is gray to almost white and
suitable for both building and monumental uses. At West Point,
Orange County, dark-gray gneiss has been quarried for construction of
the Military Academy buildings.

GRANITE 137

Near Yonkers a light blue to reddish granite with gneissoid foliation
is obtained for rough construction work. Similar banded granites for
rough building are quarried at various points near New Rochelle. Rock
for building and monumental use occurs near the Bronx. Much of the
granite in this area north of New York is useful as rock-faced ashlar for
residential building.

California. — Production of block granite in California was valued at
$620,790 in 1928. About one fourth was monumental and three fourths
building stone. The value of building granite has fluctuated greatly.
In 1925 it reached a high point of $1,200,000 but declined to less than one
sixth of that amount in 1928. A large proportion is used in San Francisco
and Los Angeles, therefore the demand depends to quite an extent on
local conditions. Paving, curbing, and rubble production was very
small in 1928 but increased greatly in 1929 and 1930. Total production
in 1929 was valued at $1,560,314; in 1930, $1,047,256; in 1936, $247,967;
and in 1937, $78,412.

During recent years granites for building and monumental uses have
been produced in Fresno, Imperial, Madera, Nevada, Placer, Plumas,
Riverside, Sacramento, San Diego, and Tulare Counties. A high-
quality, medium-grained building and monumental granite, light gray
specked with brilliant black mica crystals, is produced at Raymond,
Madera County. It has been used widely in San Francisco for residences,
hotels, banks, and State and Federal buildings and also quite extensively
for monuments and mausoleums. The granite near Rocklin, Placer
County, is light gray and of fine- to medium-grained texture ; it is used for
buildings and monuments, chiefly the latter. At Porterville, Tulare
County, near Perris, Riverside County, and also in Fresno and Plumas
Counties fine-textured, dark blue hornblende diorites classed as black
granites are quarried for monumental uses.

Near Lakeside, San Diego County, a fine-grained, light gray granite
known as "Silver Gray" is quarried for monumental and other orna-
mental work. Granite is also produced in this county at El Cajon,
Escondido, Santee, and near Temecula, the latter locality providing a
dark blue rock. Building and monumental granites are obtained at
Corona, Riverside, and Wineville, Riverside County, and near Academy,
Fresno County. Granite for levees and reclamation work is quarried at
times near Andrade, Imperial County. Monumental stone is quarried
at Nevada City, Nevada County, and near Chilcoot, Plumas County,
that from the latter place being sold as "Light Pearl." A quarry at
Folsom, Sacramento County, provides stone for the construction of
prison buildings.

Maryland. — Block granite produced in Maryland in 1928 was valued
at $430,946, or 1.7 per cent of the total production value for the United
States. About 87 per cent in value was used for structural purposes,

138 THE STONE INDUSTRIES

chiefly as rough building stone, about 10 per cent as rubble, and the
remainder as curbing and paving stones. The building-granite industry-
has grown from a value qf less than $50,000 in 1919 to nearly $400,000
in 1928. Production in 1929 was valued at $229,080; in 1936, $44,955;
and in 1937, $190,546.

The Maryland granites are confined to a belt running north-east from
the Potomac River to the Pennsylvania border, the southern end of the
belt extending from Washington, D. C, to a point near Seneca. It
occupies a position on the eastern slope of the Piedmont Plateau bounded
on the east by the gravels and clays of the Coastal Plain and on the west
by the less crystalline rocks of the western Piedmont slopes. Within
this zone granite is prominently developed in about 15 areas, and in at
least 5, quarries of considerable importance have been developed. The
more important commercial deposits are the granites of Cecil and
Baltimore Counties and the granite gneisses of Baltimore and Mont-
gomery Counties.

Granites of Cecil and Baltimore Counties. — At Port Deposit, Cecil
County, about 3 miles above Havre de Grace on the Susquehanna River,
a light bluish gray biotite granite occurs. A noticeable feature of the
rock is a secondary gneissic structure which is due to parallel arrangement
of the mica flakes. It is uniform in texture and color, and quarry condi-
tions are favorable. Moderately spaced joints are in three systems, two
at about right angles to each other, while the third intersects the major
series at about 60°. Quarrying is facilitated by sheeting planes. The
granite is used principally for building purposes, such use dating back to
1816 and 1817 when large stones were supplied for abutments of a bridge
across the Susquehanna River.

An attractive gray biotite granite, widely used for general building
purposes and to some extent for memorial stone, occurs northeast of
Woodstock over the county line in Baltimore County. Well-defined
sheeting planes dip 10 to 15°, but jointing is somewhat irregular.

Gneisses of Baltimore and Montgomery Counties. — A dark to blue-gray
biotite gneiss occurs near Baltimore. Conditions favor quarrying, as
sheets dipping 30 to 40° are 4 inches to 5 or 6 feet thick, joints are in two
series approximately at right angles and moderately spaced, while the
grain (rift) is vertical and nearly parallels one of the jointing systems.
The rock breaks out so readily into cubical blocks that scarcely any
explosives are necessary. It is used chiefly for rough construction in and
about Baltimore.

In southern Montgomery County a similar dark gray granite gneiss is
used for bridge, house, chimney, and foundation building. It is so well-
supplied with joints and sheeting planes that it is easily quarried. Iron
oxide stains in the joints provide attractive nonfading colors for "seam-
faced granite." Several bridges on the new Mount Vernon Highway and

GRANITE 139

many other artistic structures including numerous residences in and near
Washington, D, C, are built of stone from these quarries.

Rhode Island. — Granite in the form of dimension stone produced in
Rhode Island in 1928 was valued at $413,707, or 1.7 per cent of the value
of total production for the United States. Monumental stone dominates
the industry, amounting to 92 per cent in value of the total for 1928.
About 4.4 per cent was used for building and 3.6 per cent for curbing.
Production of building granite was much greater during pre-war years
than now. Production in 1929 was valued at $348,173 ; in 1930, $366,602;
in 1936, $292,577; and in 1937, $320,712.

The industry is centered in and near Westerly and Bradford, Washing-
ton County. The deposits are unusual, in that they take the form of
massive dikes 50 to 150 feet thick intruded into the older granite gneisses,
which dip 30 to 45° to the south. The chief j oint systems run N. 10°-25°E.,
though various other systems have been noted. The rift is horizontal or
slightly inclined, and the grain is vertical or nearly so. Three main types
of commercial granite occur: "Westerly Pink," sometimes called
"Westerly Statuary," a pinkish or buff biotite granite (quartz monzonite)
of very fine uniform texture; "Blue Westerly," a bluish gray biotite
granite of fine, even-grained texture; and "Red Westerly," a reddish gray
granite speckled with black, having an even-grained medium, inclining to
coarse, texture. "Westerly Pink" and "Blue Westerly," the fine-
grained rocks, are used for monuments, and the coarser-grained red rocks
for construction. The pink and blue varieties take a high polish and are
attractive in color and texture. They are well-known to the monument
trade and have been widely used for many years.

Connecticut. — The value of block granite produced in Connecticut in
1928 was $396,344, or 1.6 per cent of the value of production for the
entire country. About 61 per cent was devoted to monumental purposes,
23 to building, and 16 to curbing. Production in 1929 was valued at
$710,739; in 1930, $496,124; in 1936, $144,108; and in 1937, $233,059.

Granites, granite gneisses, and related rocks occur in many parts
of the State, and their geologic relations are complex. Production of
dimension stone is confined chiefly to four counties — Hartford, New
Haven, New London, and Windham.

Hartford County. — Near Glastonbury a biotite granite gneiss occurs
in nearly horizontal sheets up to 3 feet thick. The rift follows the folia-
tion, dipping about 10° in a direction N.50°W. The rock is well-adapted
for rough construction and curbing, and the products are sold chiefly
in Hartford.

New Haven County. — Near Ansonia a blue-gray muscovite-biotite
granite gneiss is quarried for rough construction and curbing. The most
important quarries of the county are near Branford and Stony Creek.
The "Branford Red" rock is a reddish gray biotite granite gneiss of

140 THE STONE INDUSTRIES

medium to coarse, irregular texture. It is an attractive building stone
and has been used widely in many important structures; it is also
employed to a limited extent for monuments and curbing. "Branford
Pink" is another type produced in this district. "Stony Creek Red" is a
reddish gray coarse-grained gneissoid granite used for buildings, monu-
ments, and mausoleums.

New London County. — The most important granite quarries of Con-
necticut are in southern New London County near East Lyme, Groton,
Millstone, Niantic, and Waterford. At East Lyme and Niantic an even-
grained, pinkish gray granite provides an attractive monumental stone
sold under the name "Golden-Pink Niantic." Like the Westerly (R. L)
granite it occurs as a dike, in this instance about 40 feet thick intruded
into a gneiss. At Groton a fine-grained, greenish gray granite is quarried
for monuments. Production is most active in the Millstone and Water-
ford districts. "Millstone" granite which is available to both rail and
water transportation is a fine-grained, dark gray stone used for monu-
ments, paving stones, curbing, and to a limited extent building stone.
At Waterford the rock is buff-gray, but the hammered face is light gray.
It takes a fine polish and is marketed as "Connecticut White," being used
as an architectural stone, for monuments, and for paving stones. Like
the other granites of this district it occurs in dikelike masses.

Windham County.— A biotite granite gneiss is quarried near Oneco in
southern Windham County near the Rhode Island line. "Oneco" is an
attractive fine-grained, dark bluish gray stone used for building purposes
and for curbing.

Pennsylvania. — Granite dimension-stone production in Pennsylvania
in 1929 was valued at about $383,500. About 70 per cent of this amount
was building stone; 22, monumental; 6, rubble; and 2, paving stones.
The 1928 figures were not representative. Production in 1930 was valued
at $359,045; in 1936, $263,287; and in 1937, $268,859. Pennsylvania is
unique in that large quantities of granite gneiss are quarried for house
construction and other local uses, particularly in the Philadelphia district.
Figures as reported are probably low because a great number of small
operators do not submit reports.

Monumental Granites. — Diabase and gabbro, classed as "black
granites" are produced in small quantities in Berks County, and in larger
quantities in Bucks and Chester Counties. Black granite has been
quarried in Bucks County near California — "French Creek Black" at
Roedey and "Blue and Dark Pearl" at Shelly — but recent production
has been chiefly from the Coopersburg district. A jet-black stone show-
ing splendid contrast between polished and tooled surfaces is marketed as
"Bonnie Brook Black Granite." Similar stone is produced near Saint
Peters, Chester County.

GRANITE 141

Building Granites. — Practically all the rock classed as building granite
is an attractive, durable, dark granite gneiss which occurs abundantly in
many parts of Philadelphia and Delaware Counties and to some extent in
Montgomery, Chester, and Bucks Counties. None of the quarries are
large, though some provide considerable tonnage for use in and about
Philadelphia. In many places stone excavated in digging cellars is used
for foundation work and even for buildings. The extensive use of these
gneissic rocks has had a marked influence on the architecture of the
Philadelphia district. Some of the buildings have withstood weathering
influences remarkably well for more than 140 years.

South Dakota. — The value of block granite produced in South Dakota
in 1928 was S220,898, or 0.9 per cent of the value of total production for
the United States. Practically the entire amount is classed as monu-
mental stone. Before 1925 South Dakota was a producer of granite in a
very small way, but since that date the industry has grown rapidly.
Production in 1929 was valued at $280,245; in 1930, $397,047; in 1936,
$406,115; and in 1937, $547,334.

Production is confined almost exclusively to Grant County, where
about five companies operate. The deposits are part of the granite belt
of the upper Minnesota River Valley, which is described in the section
on Minnesota, and the rock quarried near Milbank and Bigstone City is
similar to that near Ortonville and Odessa, Minn. It is sold under the
trade names "Hunter's Mahogany" and "South Dakota Mahogany."
Some of the stone is shipped in rough blocks to finishing plants in Orton-
ville, Minn.

Rushmore Mountain, in the Black Hills of South Dakota, has been a
center of interest since 1929, when Congress authorized funds for carving
a gigantic memorial on the granite mountain face. A brief story of Our
Country written in part though not completed by Calvin Coolidge will
be carved deeply upon an entablature 80 feet wide and 120 feet high;
accompanying this history, carved in colossal proportions, will appear
the figures of Washington, Jefferson, Lincoln, and Theodore Roosevelt.
A related project at Stone Mountain, Ga. is described under the granites
of Georgia.

Texas. — Block-granite production in Texas in 1928 was valued at
$191,084, or 0.8 per cent of the value of total production for the United
States. Production in 1929 was valued at $165,807 ; in 1930, $220, 189 ; in
1936, $66,708; and in 1937, $52,361. The industry is confined chiefly
to Llano, Burnet, and Gillespie Counties in the west-central part of the
State. Llano, the most productive county, is the source of a fine- to
medium-grained, light to dark gray granite which is used almost entirely
for monuments. A coarse-grained red granite quarried at Granite Moun-
tain near Marble Falls, Burnet County, is well-adapted for building

142 THE STONE INDUSTRIES

purposes and was used for the construction of the Texas State Capitol at
Austin. It is also used for jetties, breakwaters, and other wave-resistant
structures and employed to a limited extent for monuments. Near
Fredericksburg, Gillespie County, an attractive red monumental stone is
quarried. Most of the products are sold within the State, though some
are shipped as far as New York City.

Other Producing States. — The 16 States discussed in the preceding
pages provide nearly 96 per cent of the production of granite as dimension
stone in the United States. Most of the remaining 4 per cent is reported
from six States — South Carolina, Colorado, Oklahoma, Delaware,
Montana, and Washington. In production value some of these States
exceed members of the minor group of eight States previously described,
but the number of producers is so small that production statistics have
been withheld to avoid revealing individual figures.

An attractive fine-grained, gray biotite granite quarried at Rion,
Fairfield County, S. C, is sold widely for monuments under the trade name
"Winnsboro Blue."

Colorado also produces attractive monumental granites valued at
more than $200,000 a year. Chief production is from Salida, Chaffee
County, where a fine-grained, dark blue-gray quartz diorite is sold under
the names "Salida Blue" and "Salida Dark Gray." Monumental stone
is also obtained in Fremont County.

Oklahoma and Montana are producers of monumental granite, and
Delaware supplies a rough construction stone similar to that produced in
eastern Pennsylvania.

An attractive dark red granite or syenite is quarried near Graniteville,
Iron County, Mo. The products are monumental stone and paving
blocks, the former being marketed widely as "Missouri Red "

A light gray granite has been quarried quite extensively in Little
Cottonwood Canyon about 20 miles from Salt Lake City, Utah, and used
for building purposes in that city.

Block-granite production in the State of Washington ranges from
$10,000 to $50,000 a year in value. The most important production
center is Medical Lake, Spokane County, where a fine- to medium-grained,
light gray granite is quarried, chiefly for the manufacture of memorial
stones. A small production of building and monumental granite is
reported at times from Index, Snohomish County.

Volcanic tuffs and related rocks are used to some extent for building
in Idaho, Arizona, New Mexico, Nevada, and California. Those in
Idaho have been described by Behre.^'^ The Arizona State Capitol and
several buildings of the University of Arizona are built of tuff. An

2^ Behre, C. H., Jr., Tertiary Volcanic Tuffs and Sandstones Used as Building
Stones in the Upper Salmon River Valley, Idaho. Contributions to Economic
Geology, pt. 1, 1929, U. S. Geol. Survey Bull. 811-E, pp. 237-248.

GRANITE 143

ash-gray tuff weighing only 65 pounds a cubic foot occurs near Pioche,
Nev. Nails may be driven into it almost as easily as into wood. Porous
tuff and pumice are cut into blocks and used as natural light-weight
building materials.

QUARRY METHODS AND EQUIPMENT

Choice of Location.— Granites occur widely in many States. Single
masses, as indicated by numerous related outcrops, may extend over
thousands of square miles. However, relatively few of these occurrences
have the qualities, locations, or working conditions requisite for adapt-
ability to industrial uses. Nature has been the fabricator of the rocks,
and man is powerless to change the inherent qualities of native beds;
therefore, selection of an area of rock with qualities suitable for industrial
uses is of paramount importance. First, outcrops should be examined
carefully. If a mantle of overburden hides the surface of the rock it may
be trenched, but adequate study can be made only when it is removed.
Stripping may be done by any method described in a previous chapter.
Some quarrymen recommend examination of rock during or immediately
after a rain, because hair lines, streaks, and knots ai^e recognized more
easily on a wet than on a dry surface. Areas chosen for quarrying
usually include masses of rock of uniform texture, attractive color, and
relative freedom from irregular or closely spaced seams and from dikes,
knots, or hair lines. Requirements for monumental and polished archi-
tectural stones, are most rigid; but more liberal variations in color and
texture are permissible for building, paving, and curbing granite, while
rock of quite uneven texture and color, such as the gneisses and schists,
may be used for rubble and other rough-faced types of building stone.

Plan of Quarrying. — The position and direction of quarry walls
usually are governed by the joint systems, because an open joint usually
constitutes a "heading" or quarry wall. Quarrying conditions are most
favorable where two systems of vertical joint seams are at right angles to
each other, as this permits easy development of a rectangular quarry
opening and the production of rectangular blocks. Many granite
deposits occur as domes rising above the general level, permitting wide and
shallow quarries, with easy access. This type of quarry has many
advantages, particularly in New England because the sheeting planes,
which assist greatly in separation of blocks, are almost invariably much
closer together near the surface than at depth. A typical bench or shelf
quarry is shown in figure 23. In some places quarries are sunk to depths
of 200 feet or more. Deep quarrying may be occasioned by restricted
property lines or by improvement in the quality of the rock at depth.
The plan of quarrying may be influenced by dikes or other structures.

Quarry Operations. Drilling. — Drilling greatly exceeds every other
quarry operation in importance, for granite is so hard that no tools but

144

THE STONE INDUSTRIES

drills can cut it in a quarry. Hand-sledged drills date back many years
but have been gradually superseded by steam-driven reciprocating drills.
The latter types, both steam- and air-driven, are still in use, but com-
pressed-air hammer drills are most common in modern granite quarries.
Drilling equipment has been improved greatly during recent years. The
increasing rate of drilling is due in part to the use of better machines and
in some measure to the employment of highly efficient mechanical drill
sharpeners. A modern quarry blacksmith shop is a marvel of speed and
accuracy in reconditioning drill bits.

The principal constituents of granite are, with the exception of mica,
as hard as, or harder than, steel, hence drill bits dull rapidly and lose their

Fig. 23.

-A typical bench or shelf granite quarry in Vermont with convenient railroad
transportation.

gage as a result of abrasion of the outer edges. Therefore, after depths
of 2 to 4 feet are attained steel is changed, and with each change a bit
M to }{q inch smaller is used. In general practice, many holes are
drilled 12 to 15 feet deep, and depths of 20 to 30 feet are not uncommon.
Starting bits are l^i to 2^i inches in diameter on the cutting end; the
larger size is used for deep drilling.

A great advance in drilling practice was attained with the invention
of hollow steel. Exhaust air passes down the hole in the center of the
bit and blows rock dust from the cutting edges, promoting effective work.
Air-operated devices for feeding the bit downward and for lifting the drill
head when steel is changed have reduced greatly the physical labor and
increased the speed of drilling.

GRANITE 145

The drilling rate in granite is slower than in most rocks. At Westerly,
R. I., thirty 4-foot holes a day is a fair average rate attained with a
tripod reciprocating drill using a 1^^- to 2-inch bit. At Barre, Vt. each
bar-drill machine averages 100 to 120 linear feet a day for moderately
deep drilling, using a 2,^:4-inch bit as a starter. Exceptional rates of
175 to 200 feet a day have been attained.

A bar drill is a type of equipment which has long been used but
recently has been greatly improved. A horizontal bar 12 to 14 feet long
is supported by a pair of steel legs at each end. A heavy hammer drill is
mounted on the bar and may be moved quickly to any desired position by
means of a pinion working in a rack of cogs extending the full length of
the bar. The chief function of this drill is to make rows of closely spaced
holes exactly in line and in one plane. A four-point hollow steel bit
generally is used. Reciprocating drills mounted on tripods are sometimes
used for deep drilling, and are occasionally used on bars.

For shallower holes used in plug-and-feather wedging hammer drills
held in the hands usually are employed. The ordinary hammer drill,
with a six-point bit and automatic rotating device, is used for "foot
holes," a name applied in Vermont to holes 1 or 2 feet deep. Hand-held
hammer drills are also used for putting down deep single holes or small
groups of holes for blasting. These are much lighter in weight than
the machines used on bars, and the drilling rate is somewhat slower,
averaging 75 to 100 feet a day.

For holes 4 to 6 inches deep and about ^^ inch in diameter a smaller
type, known as a "plug drill," is used. Valve action depends upon
pressure of the bit, therefore it operates only when the steel is pressed
firmly against the rock. The bit, usually of the chisel-point type, is
rotated by a hand wrench or automatically as a result of special
sharpening.

Reaming. — A reamer is a flanged tool driven into a drill hole to cut
grooves on opposite sides. Reaming greatly assists blasting, especially
by the Knox method, mentioned in its application to granite quarrying
under Blasting. It may also be employed to assist straight splitting
when the wedging method is followed.

Broaching. — Broaching is the process of cutting out webs or "cores,"
as they are sometimes called, between closely spaced drill holes to make a
continuous channel. A broaching tool resembles a flattened drill bar.
The cutting end is about 3 or 3)^^ inches wide and \}i inches thick,
sometimes with transverse ridges on the face. It may be used in a drill
head. After a row of holes has been completed the full length of the bar
broaching tools are substituted for drills, and all cores or webs between
holes are cut away. Broaching is usually slow and with increasing depth
becomes even more laborious, for as drill holes become smaller the cores
or webs become correspondingly wider.

146 THE STONE INDUSTRIES

Blasting. — Blasting is commonly employed to obtain large fractures,
but great care must be exercised in the use of explosives to avoid shatter-
ing the rock. Dynamite is used for breaking up waste rock, but in good
granite the slower-acting black blasting powder is invariably employed.
A charge is the minimum amount that will make a single fracture. If too
much explosive is used incipient fractures may be developed in quarry
blocks. Such fractures, which may be so small as to be unobservable
until the rock is polished, are doubly detrimental, as they not only cause
waste but result in condemnation of a block after much time and labor
have been spent in shaping and finishing it.

Straight, even breaks, with a minimum number of drill holes, may be
made by employing the Knox system. This involves the use of a reamer
which when driven into the hole cuts grooves about one-fourth inch deep
on opposite sides. Care is taken to cut the grooves exactly in line with
the desired direction of splitting. This system, already described in
detail in the chapter on sandstone, also involves the use of an air space
above the powder charge, which increases the effectiveness of the explo-
sive force. A uniform, straight fracture with an area greater than
100 square feet sometimes is made by blasting in a single reamed drill
hole. Occasionally several parallel holes are made, or three or four may
be drilled in a fanlike arrangement.

Wedging. — Channeling and blasting have their proper places in quarry
work; but most fractures, especially those of smaller area, are made by
wedging. Plug-and-feather wedging has been described. Small plugs
and feathers are used in ^^-inch "plug" holes 4 or 5 inches deep and

6 to 18 inches apart. They are sledged lightly in turn back and forth
along the line until a fracture is made. Plug-hole wedging is effective
in rift and grain directions, even for large breaks. A few years ago the
writer observed in a Georgia quarry a single mass of granite 8 feet thick,

7 feet 8 inches wide, and 375 feet long separated by the plug-and-feather
method with holes 5 inches apart and only 5 inches deep. If a break is to
parallel the hard way of the rock "foot holes" 1 to 1}^ feet deep are
drilled 1}^ to 4 feet apart, with plug holes between them. The longer
plugs and feathers used in the deeper holes are known as "foot wedges."
The straightest fractures are obtained when made in the center of a rock
mass. If a small piece is to be wedged from the side of a larger block the
fracture tends to run toward the lighter side. In making large fractures
the wedging process is not hurried. Plugs are driven firmly, and then
a little time is allowed for the fracture to start before sledging is resumed.

Hoisting. — Most granite quarries are equipped with derricks having
steam or electric hoists. In wide quarries where booms can not reach all
parts, stone blocks or boxes of waste may be handled beyond the boom
radius by attaching a line from some other near-by derrick, the two work-
ing in conjunction.

GRANITE 147

In New England wooden derricks with masts and booms of Oregon
pine are generally used. They are large and powerful, can handle
blocks weighing 40 or 50 tons, and in exceptional instances attain a
capacity of 80 tons. At some Maine quarries the original timber for the
boom is sawed lengthwise in the center, blocks of timber are placed
between the two parts at various points, and the halves are bolted
together through the blocks. Sheaves are mounted in the space between
the halves. Such "split" booms are less liable to warp and twist than
single timbers, and therefore the sheaves run true and do not wear the
cable. A 50-ton-capacity derrick may have a mast 100 feet high and a
boom 95 feet long. In Minnesota angle-steel derricks generally have
replaced wooden derricks. Several quarries are equipped with overhead
cableways, but their lifting capacity is usually very much lower than that
of derricks.

Quarry Methods. Influence of Physical Properties and Rock Struc-
tures.— Channeling-machine methods used in the softer rocks (limestones,
sandstones, slates, and marbles) do not apply to granite, which is an
exceptionally hard rock; hence, as previously explained, drilling is sub-
stituted therefor. As artificial cuts are costly, full advantage is taken of
open seams or "headers" for quarry or bench walls. As far as possible,
all block separations parallel the directions of easiest splitting — the rift
and grain. It is a fortunate circumstance that in many granite districts
the rift parallels one of the major jointing systems, for in the natural
development of a quarry, successive partings thus parallel both rift and
joints.

Sheeting planes or "bottom joints" greatly assist quarrying. In
fact, vertical breaks can not be made successfully until the mass is free at
the quarry floor. If open sheeting planes are provided in nature, succes-
sive masses may be removed with ease. If such bottom joints are far
apart or absent artificial sheeting planes must be made, possibly by
drilling a series of horizontal holes, sometimes termed "lift holes," and
making a fracture with wedges or by the use of explosives. The cost of
quarrying is usually relatively high in deposits where floor breaks must be
forced by wedging or blasting.

Many deposits occur in characteristic domelike form, and sheeting
planes usually are arched to parallel in a general way the surface contour
of the rock. This attitude of sheeting planes is an advantage in quarry-
ing, for as an opening is made in the side of the dome the quarry floor
slopes away from the working face, providing automatic drainage and
greatly facilitating the movement of heavy blocks of stone. Sheets are
sometimes relatively thick, and joints are spaced close together. Open-
ings in deposits having such a preponderance of joints are sometimes
termed "block quarries," because they provide massive cubical blocks.
Quarries in the St. Cloud district, Minnesota, are of this type. Con-

148

THE STONE INDUSTRIES

trasted with them are the typical quarries of New England, where sheets
are thin and joints widely spaced. In such openings the quarry face
rises in a series of low steps. The layers are usually thin near the out-
crop, gradually thickening as the quarry face is worked back into the
dome. As a rule, they also gradually thicken with depth. Openings in
rock of this type are sometimes known as "sheet quarries." Figure 24
shows the typical New England sheet structure. Exceptionally, sheeting
planes are far apart in New England quarries, for example, in some at
Barre, Vt.

Channeling. — "Channeling" in granite quarrying has quite a different
meaning than when employed in limestone or sandstone. In the latter

Fig. 24

A typical New lingland granite (iu;ui\- illut^tI■alin

Me.

^lll'(•t ^Inicture; Stonington,

rocks it is the process of making a cut with a channeling machine, whereas
in granite it refers to the drilling of a closely spaced row of holes and
broaching or cutting out the narrow webs or cores between. Cuts thus
obtained are similar to those resulting from the operation of channeling
machines in the softer rocks. This method is employed in many quarries
in preference to blasting because, although slow and more costly, it gives
a straight surface and does not cause shattering. Its advantages are
most apparent in making cuts in the hard way. Channeled rock surfaces
are shown at the top and upper right corner of figure 25.

Primary Cuts. — The first step in quarrying is to separate the larger
masses from the solid ledge. To obtain space for movement of blocks
at the quarry wall it may be necessary to cut a channel. Wall channeling
usually is done in the direction of the head grain, or hard way. Channel-
ing tight ends is sometimes difficult because the rock in some deposits,

GRANITE

149

especially those in which few joints occur, is under compression, and when
the drill holes provide a means of relief the rock expands : thus pressure
may partly close the drill holes. It is claimed that at Stone Mountain,
Ga., a mass 60 feet long will expand 2 inches.

The most difficult step in opening up a new bench on a quarry floor is
to obtain a free face from which to work. To give necessary working
space a mass of rock 3 to 5 feet wide, and the depth of the bench, must be
removed. Different methods are employed to make such a trench or

Fig. 25.

-Granite quarry at Barre, Vt., in which various methods cf driUing are illustrated.
{Courtesy of E. L. Smith & Co.)

keyway. If the mass is flanked on either side by an open seam the inter-
vening rock may be removed by drilling and blasting. If open seams
can not be utilized holes may be drilled in two parallel rows 3 to 5 feet
apart, and the intervening rock shattered with dynamite may be removed
as waste. Another method is to make two channel cuts 10 to 15 feet
apart by the process described in a preceding paragraph and to remove
the mass of rock between them. This method is less wasteful than
blasting, as the rock between channel cuts may be removed as quarry
blocks and utilized, at least in part.

A unique method is employed in a large quarry at West Chelmsford,
Mass. A drum core drill, using steel shot as abrasive, cuts a series of
holes along the center and across the ends of the quarry. Webs 8 to 10
inches wide are left between the holes to protect the drill from rock

150 THE STONE INDUSTRIES

movement occasioned by pressure. The webs are removed later with
light powder blasts, and a channel is thus formed. The circular cores,
52 inches in diameter, are cleverly utilized by quartering them for the
manufacture of corner curbstones. They are more accurate in shape
and have smoother surfaces than rough-hewn curbstones.

Separation of Larger Masses. — When an open bench has been secured
by any of the methods previously described, free faces being thus pro-
vided, the next step is to separate large masses from the solid ledge. In
''block quarries" or "boulder quarries," as they are called in Vermont,
where sheeting planes are widely spaced, primary separations may set
free blocks weighing thousands of tons. If the bench approaches 20 or
more feet in height the larger fractures are made by blasting. "Lewis"
holes 2} 2 to 3 inches in diameter are drilled several feet apart and from
one half to almost the full depth of the bench, at the bottom of which is a
sheeting plane. A fracture is made by discharging black blasting powder
in the holes according to the method described under blasting. Usually
this break is on the rift or grain. In rock which splits easily three holes
in fan-like arrangement may suffice. A series of deep holes in which
explosives have been discharged are shown in the center of figure 25.

When a vertical break is thus made the mass of rock may still be
too heavy for wedging. If so, horizontal holes are drilled at a point about
halfway down the bench face, and light charges of powder are used to
fracture the rock along the plane of horizontal rift or grain. Some
quarrymen do not favor channeling beyond a depth of 10 or 12 feet. If
sheeting planes are 20 or more feet apart the rock is removed in two
''lifts," the bottom of the first being opened with powder charges in
horizontal holes.

In "sheet quarries" where sheeting planes are close together blasting
may be required only for making primary trenches, and all subsequent
breaks are made by wedging. In such deposits quarrying usually is
simpler and less costly than in those where sheeting planes are widely
spaced.

Forcing Sheeting Planes with Compressed Air. — An ingenious method
of making artificial bottom joints is employed in North Carolina and
Georgia. Certain deposits, notably at Lithonia, Ga., and Mount Airy,
N. C, consist of low, massive domes that are unique in that one may walk
over the bare surface of the rock for hundreds of feet without finding any
indication of a joint. Sheeting planes are likewise far apart or entirely
absent. To remove the larger masses of stone it is first necessary to
make artificial floor breaks.

At one Lithonia quarry as observed by the writer, two holes of about
3-inch diameter are drilled close together to a depth of about 8 feet.
Two men may work at these holes for weeks or even months. A very
small charge of black blasting powder, not more than a spoonful, is

GRANITE 151

placed in each and tamped with clay, and the charges are fired simul-
taneously with an electric battery. The force of the explosion starts a
small fracture running outward from the bottoms of the holes. This
process is repeated time after time, with gradual increase in the size of
charges, and the fracture extends slowly. A quarryman skilled in this
type of work can readily judge the extent of the fracture, for when
standing on the surface of the rock some distance from the drill holes he
can determine from the nature of the jar when charges are fired, whether
or not the fracture has reached the point over which he is standing.
Any attempt to hasten the operation by increasing the charges too
greatly would be disastrous, as it would force a vertical or inclined
fracture and render continuance of the process impossible. Solar heat
assists the process so materially that it is deemed advisable to suspend
operations in winter.

The blasting process is continued until the outward boundary of the
horizontal fracture forms a circle with a 60- to 80-foot radius. An iron
pipe is then placed in each drill hole and the space between the pipe
and the rock filled with jute or sand bags and melted sulphur, making
a strong, airtight joint. Connection is then made with the air line,
and compressed air at a pressure of about 100 pounds per square inch is
injected through the pipes to the fracture. The effect is remarkable, for
the air pressure immediately widens and extends the fracture until it
emerges at the surface on the flank of the dome or at some distant line on
the quarry floor. A sheeting plane thus formed may cover an area of
1 or 2 acres and provide a mass of rock large enough for an entire season's
operation. The above process is modified somewhat by different
operators.

Employment of compressed air to break rock in this manner does not
bear promise of being accepted as general quarry practice, because its
application is greatly restricted by quarry conditions. Most commercial
deposits are intersected by joint systems, and obviously open joints would
provide a means of escape for explosive gases generated during the
blasting process, rendering it ineffective and also permitting escape of the
compressed air used in the final operation. Thus, the process can be
employed only in those unique occurrences where joints are very far
apart.

Subdivision of Blocks. — After large masses are separated from a solid
ledge the next step is to subdivide them into blocks of the approximate
sizes and shapes desired for finished products or into sizes convenient for
removal from the quarry. Quarrymen follow the direction of rift and
grain in making secondary and following fractures, just as they do in
primary breaks. The wedging method is used almost universally.
Wedging in plug holes may suffice to give a straight fracture in directions
of rift and grain. For subdivision of large blocks the line of plugs may be

152

THE STONE INDUSTRIES

continued down the ends, as well as along the top, as shown in figure 26.
Wedging from both ends and top tends to insure a straight split. For
breaks on the hard way "foot holes" may be put down to depths of
12 to 18 inches and 2 or more feet apart, with several shallow plug holes
between. "Foot wedges" are driven in the foot holes, and small wedges
in the plug holes. Foot holes with four intervening plug holes are shown
at the left center of figure 25, page 149. Holes sometimes are reamed for
making splits on the head grain.

Fig. 26.-

-Subdivision of a block of granite in a Westerly, R. I., quarry by wedging on top
and end. {Photo by the author.)

The above methods apply where the weight is approximately balanced,
that is, where the line of drill holes is near the center of the mass. Fre-
quently there is a demand for a relatively thin mass of rock, possibly not
more than 2 or 3 feet thick but of wide area, such as for a platform or the
roof of a mausoleum. At Barre, Vt., separating such a mass is known as
"deep holing." Holes about 6 inches apart are drilled in line to almost
the full depth of the bench, and a fracture is made by driving "foot-hole"
wedges therein; or, sometimes long wedges are used. If shallow holes

GRANITE

153

were employed the fracture would curve and run out toward the thinner
mass, but deep ones carry the fracture straight through. The same rule
applies in the subdivision of smaller blocks. In figure 27 a thin slab that
has been separated by deep-hole wedging is shown suspended in midair.
It may be observed that the block was removed from a point near the

Aj^ \^'

Fig. 27. — A thin slab of granite that has been quarried by deep-hole wedging. {Courtesy

of E. L. Smith & Co.)

center of the photograph, where plug holes for the final vertical break
appear.

An interesting modification of the wedging method is used in Rhode
Island. For making a fracture 6 or 7 feet deep holes about 5 feet deep,
spaced 1 to 13>^^ feet apart, are drilled in a row. A steam pipe with numer-
ous right-angled tees is placed parallel with the row of holes, and lengths
of hose attached to the branch pipes are inserted to the bottoms of the

154 THE STONE INDUSTRIES

holes. Live steam is blown into the holes for 1 to 2 hours, and the expan-
sion caused by the hot steam makes the desired fracture.

Products of monumental granite quarries are of two main types,
which may be designated as stock sizes and specials. The former are the
standard sizes that satisfy the majority of manufacturers' demands
for smaller monuments supplied to the retail trade. As they may be kept
in stock quick delivery is assured. Specials are cut to order and may
be large or small. Most of them are used in larger, more expensive
monuments and mausoleums. They may be made up of 10, 12, or a
greater number of stones of different sizes and shapes, cut to size after an
order is received. The larger companies usually have a variety of blocks
on hand or have benches in the quarry available from which desired sizes
may be cut with little delay.

Removal of Stone from Quarry. — Several diverse methods are used for
removing granite blocks from a quarry. In wide, shallow quarries, like
those at Mount Airy, N. C, and Lithonia, Ga., standard-type tractors,
caterpillar tractors, auto trucks, or two-wheeled mule carts are employed.
For handling moderate-size blocks a caterpillar derrick crane may be
used. Derricks are usually employed for deeper, narrower quarries.
Derricks usually are placed in the most convenient positions for loading,
and for taking full advantage of a sloping quarry floor if such is
present.

As mentioned previously the tendency of sheeting planes or rift to
dip downward from the quarry face is of great advantage in removal of
blocks. At some quarries, notably at Stone Mountain, Ga., the quarry
floor is so steep that blocks slide to the lower edge, where they are lifted
by large derricks to standard flat cars for transportation to the mill.

Some New England water-front quarries are so convenient to docks
that derricks may place blocks directly on barges. Others have some
means of intermediate transportation, and supplementary loading der-
ricks are provided at the docks.

Service Yard. — The aim of the quarryman is to produce either
blocks of special sizes cut to order, or standard blocks that may be
marketed readily. In the course of quarrying many odd-size or irregular
blocks are produced ; others may contain imperfections in color or texture
in certain places only, necessitating the removal of defective parts. By
consulting his order sheet the yard foreman may find that certain special,
or smaller standard sizes can be obtained from irregular or defective
blocks with minimum waste, and some companies maintain what is known
as a "service yard" on the quarry bank where such blocks are subdivided
to best advantage.

Quarry Haulage. — Where quarries are on the water front direct
loading on barges is possible. Sometimes mills are so close to quarries
that little or no intermediate transportation is required, but generally

GRANITE 155

they are some distance from quarries. As granite usually is quarried in
large blocks standard railway cars and locomotives ordinarily are
employed for conveyance. Locomotive cranes are very convenient, as
they not only haul cars but load and unload blocks. This type of
conveyance is used at Westerly, R. I., and in other districts. Where the
distance from quarry to mill is short (as at Mount Airy, N. C.) overhead
cableways are used both for hoisting blocks from quarries and conveying
them to the mills. Wagon and truck haulage is used to a limited extent.

Disposal of Waste. — Waste at granite quarries results from many and
varied causes. Some of it is "sap rock," which consists of weathered or
stained material bordering open seams and extending into the rock from
a few inches to 2 or more feet. Irregular or closely spaced joints, as well
as dikes, streaks, knots, hair lines, or poor color, are common causes of
waste. Much rock is lost during manufacture. At Barre, Vt., waste
constitutes 80 to 85 per cent of gross production.

Disposal of waste is a difficult problem at many quarries. Some
operators have developed a market for part of it. At quite a number of
quarries waste is crushed and sold for road stone and concrete aggregate,
and large masses are sometimes sold for riprap. Other owners are using
the waste from the high-priced products to make cheaper materials, such
as ashlar and rubble, but success in such enterprises may be expected only
where there is a potential market within reasonable distance.

If a great volume of waste must remain unutilized it usually must be
hauled some distance, for if piled close to the excavation it may impede
future development. Various means of transportation are employed,
and alert quarrymen are constantly trying to simplify operation and thus
reduce costs. A common method of conveyance is by cable cars on
inclined tracks leading to the top of the waste heap, the tracks being
extended as the size of the pile increases. Many cars have automatic
trips that dump loads endways or sideways, and the expense of keeping,--
laborers continually at work on the waste heap is thereby avoided. In
many places overhead cableways, usually with self-dumping skips, have
been successful. Waste often is used to advantage in the neighborhood
of quarries and mills to improve harbors, to level low places, to build
roads, or to provide ballast for railways.

To most quarrymen elimination of waste is obviously of primary
importance; and much attention is being given to thorough understanding
of the splitting properties of stone, to efficient sawing and surfacing
equipment, and to the most complete utilization of the rock for a variety
of products.

Manufacture of Curbing. — The manufacture of curbing commonly is
conducted on the quarry floor or in an adjacent yard. Blocks usually
are split on the rift and grain to the desired thickness and depth, plugs
and feathers being used in small, shallow drill holes. Curb-stones are

156 THE STONE INDUSTRIES

of two types — straight and corner; the latter are, of course, curved.
Corner curb is the most expensive to make, as more stone is required than
for the straight and more labor needed for splitting and dressing. An
experienced worker can make a curved split. The part of the stone that
appears above the ground or pavement when a curb is placed in position
is dressed to a smooth surface, usually with a pneumatic tool, the rougher
projections first being removed with a hand tool and hammer; the part
that remains underground may have a much rougher surface. Specifica-
tions for size and surfacing differ in various cities.

Manufacture of Paving Blocks. — Paving blocks, like curbing, usually
are manufactured in or near the quarries. Blocks are subdivided by
driving plug-and-feather wedges in shallow drill holes, and the directions
of rift and grain are followed carefully because splitting is easier and stone
split in the directions of natural cleavage has smooth surfaces that require
little trimming.

A "bull wedge" is sometimes used for final subdivision. An air-
driven chisel-edged tool cuts a shallow notch parallel to the direction in
which the rock is to be split. Two iron "feathers" are placed in the
notch, and a short, blunt, steel plug is placed between them. One blow
on the plug or "bull wedge" with a sledge will split the block and provide
smooth, uniform surfaces. It is claimed that by such means a good
break can be made to parallel the hard way. The manufacture of paving
blocks is entirely a hand process that has changed little or none in the past
50 years. Stonecutters become very proficient in determining the
directions of rift and grain and in the use of tools.

Paving stones are made in a variety of sizes, and there have been
attempts to standardize and reduce the number of sizes. Market
quotations in New York usually specify 30 blocks a square yard. Specifi-
cations for granite paving blocks have been published by the American
Society for Testing Materials. ^^

Quarry Costs. — The cost of quarrying granite varies considerably,
depending upon quarry conditions, proportion of waste, and methods
employed. A detailed study by the United States Tariff Commission,
the results of which were published in 1929 (see bibliography at end of
chapter), reveals useful data relative to the monumental granite industry.
The average direct cost f.o.b. quarry for selected operations in Ver-
mont, Massachusetts, and Pennsylvania was found to be S2.07 a cubic
foot of unmanufactured stone.

MILLING METHODS AND EQUIPMENT

Some companies quarry only and sell rough blocks to finishing mills;
others own both quarries and mills; while a third group operates mills
only, buying rough blocks from quarry companies.

" A.S.T.M. Standards 1927, pt. 2, pp. 445-450.

GRANITE 157

Rough blocks of stone constitute the raw material handled in granite-
finishing plants. At first sight it might appear that rock, a commodity
so plentiful in nature, is quite ordinary and inexpensive, but the superior
quality demanded for monuments and ornamental building stone
requires such careful selection and preparation that costs are com-
]mratively high. First-class monumental granite in unfinished blocks is
worth $3.50 to $5 a cubic foot. The fabricator, therefore, must utilize
his material to best advantage, eliminate waste as much as possible, and
exercise skill and judgment in every operation, for mistakes are difficult,
if not impossible, to correct.

The granite-finishing plant of 30 or 40 years ago was a shed in which
blocks were dressed to desired sizes, shapes, and surface finish almost
entirely by hand. Machinery has gradually replaced many hand opera-
tions, and mechanization has increased with accelerating speed during
the past 10 years. Practically every large granite-cutting plant is now
equipped with pneumatic surfacing machines, saws. Carborundum
machines, lathes, and polishing machines. However, even in the best-
equipped mills, many operations must be classed as hand cutting.

Hand Cutting. General Processes. — Hand cutting includes the use of
hand tools and hammers, and also of pneumatic tools and surfacing
machines that are power-driven but guided over the surface by hand. A
rectangular block, as it comes from the quarry, is known as a "pattern."
It is raised and supported on timbers at a height convenient for working.
The cutter first studies the working drawing of the stone to be cut,
observes all dimensions, and measures the pattern to see that it will
make a block of the size and shape indicated on the diagram. He then
squares the upper surface and removes projections to an approximate
level, then the surface is smoothed, first with the coarser tools and then
with those that give a finer finish. When one surface is completed the
block is turned, and the other surfaces are smoothed in succession, each
being squared accurately with those already finished.

A variety of tools is used in cutting granite. Some are the property
of the cutters, while others are supplied by the company. They differ
in shape and in temper of the steel from those employed for the softer
limestones and marbles, though they may have the same names. Cutting
granite is in effect a crushing process, as the impact of a hammer on a tool
causes hard, brittle minerals to crumble into small fragments or dust.
The wooden mallets commonly used in driving tools for dressing softer
stones, are ineffective on granite, where sturdier implements are required.
The granite cutter's hand hammer is of steel weighing 2}4 to 4 pounds,
with faces hardened by tempering. The heads of cutting tools are
bluntly tapered and slightly rounded on the ends, which are also hardened
so that no burr results from continued hammering. Various hand and
pneumatic tools used in dressing granite are shown in figure 28. Each

158

THE STONE INDUSTRIES

tool has its special function and has been perfected by many years, even
centuries in some instances, of practical experience.

Granite cutting may not be so fine an art as metal machining or
cabinet making, but angles and dimensions must be reasonably true. In

HAND TOOLS

Peen Hammer

Point Chisel Chipper Hand Set or Tracer

Pitching Tool

Wedge and Shims

Scotia Hammer

Hand Plug Drill Bull Set Striking Hammer

PNEUMATIC TOOLS

Surfacing Machine Tools

Fig. 28. — Granite cutting tools. {Courtesy of Federal Board for Vocational Education.)

fine building and mausoleum work tolerances may not exceed one thirty-
second inch and rarely are restricted to one sixty-fourth inch.

Pneumatic tools are guided by hand, but the impact is supplied by
compressed air. The tool strikes very rapid blows which require no

GRANITE 159

effort by the workman; he therefore can direct his entire attention to
guiding it in the proper course. Much greater speed is attained by use of
such tools than hand hammers.

A "bull sett," one of the most useful tools employed in granite
dressing is a heavy, blunt-edged hammer held in position by one man
while struck with a sledge by another; it is used for removing irregular
ends, which may extend 6 inches or 1 foot beyond required dimensions
or for breaking sawed slabs transversely. The removal of unnecessary
rock by spalling is known locally as "pitching off." Skill in manipula-
tion, as well as keen understanding of the rift or grain of the rock, is
essential when using a bull sett, as a mistake in judgment resulting in a
spall breaking beyond the line ruins a block for its intended use.

Operation of Surfacing-machine. — While surfacing-machine work
may logically be classed with hand operations it is sufficiently distinct
to justify consideration in a separate section. It involves "roughing
down" surfaces to a comparatively uniform condition. The first step
in manufacture is termed "lining" and involves working the edges of a
block to required dimensions, usually with pneumatic chisels. The next
step, known as "pointing" or "surfacing," is to dress the faces to edge
dimensions with hand tools and hammers or, when surfaces are large
and rough, with a surfacing-machine.

The machine consists essentially of a cutting head mounted on a
horizontal swinging arm which can be raised or lowered to different
working levels. Cutting tools fit into the nose of the cutting head and
are driven against the stone by rapid blows of an air-driven piston ham-
mer. An operator guiding the tool over the surface of the stone repro-
duces the hand-pointing process on a larger scale and about five times
as fast. As the cutter travels over the rock it chips off fragments,
gradually working down to an even surface. A heavy tool removes the
larger projections, followed by various smaller types to finish the surface.
Common surfacing-machine tools are illustrated in figure 28.

A surfacer has numerous applications, such as smoothing rock before
polishing, smoothing curved or cylindrical surfaces, and recessing panels.
It may be employed for rough, heavy moldings and flutings. A four-
point tool, which has a square face consisting of four blunt projections,
generally is used for recessing and shaping, or for reducing surfaces to an
even plane before polishing. If a hammered-surface finish is desired
a bush hammer is used in the surfacing-machine. The latter consists
of a series of parallel steel plates, and the tools are graded 4, 8, 10, and
12, according to the number of plates, 12 giving the finest surface.
Building and mausoleum stone usually has a 10-cut surface, while a 12-cut
is preferred for monuments.

A screen of wire netting commonly protects workmen from flying
fragments of stone. As much dust is produced dust collectors usually
are provided.

160 THE STONE INDUSTRIES

Carving. — Carving is a hand operation that demands skill and experi-
ence. It is essentially the same process described in some detail under
limestone, though granite works much more slowly. A variety of
pneumatic tools is used. As a rule, fine-grained granites are best-adapted
for carving, though there are notable exceptions. Much of the intricate
carving and lettering formerly done entirely by hand is now accomplished
by sand blasting.

Sand Blasting. — Sand blasting marks an advance in the art of granite
carving comparable in importance to the advent of explosives or of
compressed-air drills in rock quarrying. It is more precise, capable
of greater detail, and much more rapid than any other carving
process.

A polished-rock surface is first coated with a molten rubberlike or
gluelike compound, known as "dope," which hardens to a tough, elastic
consistency. Lettering and other designs are imprinted on the surface,
and with a small sharp tool like a scalpel the coating is removed from all
parts that are to be cut below the surface. The cutting of symmetrical
designs, rose petals, ivy leaves, and trailing vines requires artistic talent
and infinite patience, but carving is accomplished much more expeditiously
in the rubbery compound than in solid rock.

Stone thus prepared is placed in an illuminated closed chamber in such
a position that the surface to be carved is vertical and faces the operator,
who observes it through a window. A nozzle, through which compressed
air at a pressure of 80 to 100 pounds per square inch drives a stream of
fine sand, or more commonly powdered Carborundum, is held through a
curtain which protects the operator from the abrasive dust. The sand
blast is directed against the design, and curiously enough the exposed
hard granite is quickly cut away while the sand has little or no effect
on the soft coating. Certain parts of letters or designs may be cut
}4 to 1 inch in depth. The precision and fineness of detail are remark-
able. Rose petals may be cut so thin that they are almost transparent.
In its higher refinements sand blasting may be done in successive steps.
Petals or leaves may be depressed to varying degrees, covered with a
protective coating, then outlined by deeper cuts. A screen background
produces a series of deep holes in lines resembling a honeycomb. The
delicate and exquisite detail attained would be impossible with hand
tools, and the time required is reduced to a mere fraction of that which
hand carving demands.

Mechanical Equipment. — Machines that have replaced the slow
laborious hand work employed 30 or 40 years ago cover three main
processes — sawing, smoothing, and polishing. Although much toil
has been eliminated in these important processes and production per
man has increased enormously since machines were introduced, improve-
ments constantly are being made.

GRANITE 161

Sawing. — In the early days of granite working drilling, blasting, and
wedging were the only known means of subdividing blocks. Granite is
difficult to saw, but many years of experiment have developed machines
that give effective service. Saws have been used occasionally for a
number of years but have been generally accepted only during the past
10 or 15. There are now two well-recognized methods of sawing granite
— with gang saws and with circular saws.

Gang saws similar in construction and operation to those described
in the chapters on sandstone and limestone are used most widely. The
frames of some saws travel back and forth in a straight line; others have
the swinging motion so common in limestone sawing. The blades are
one-half to five-eighths inch thick, with notches about a foot apart in the
lower edge to carry steel-shot abrasive beneath them. The rate of cutting
is 4 to 9 inches an hour. Most modern saw beds are equipped with
concrete sumps, in which used shot are collected and elevated mechan-
ically to a box above the saws for redistribution. Several blades may be
used, and as the frame holding them is carried downward by a worm
gear a block may be cut into slabs at one operation.

Circular saws for cutting granite are 5 to 12 feet in diameter and
provided with detachable notched-steel teeth. An abundance of water
is supplied, and steel shot are fed to the blade continuously. Some saws
are provided with automatic shot feed. Granite blocks are mounted
end to end on cars and the spaces between filled with plaster of paris
to keep the shot in the cut as the saw passes from one block to another.
Cars carrying blocks are conveyed slowly beneath the saw, and operation
is therefore continuous. Sawed slabs or blocks are removed and empty
cars lifted with an overhead crane, carried back to the starting point,
and placed on the track again. The rate of travel ranges from l^-i to as
high as 5 inches a minute; therefore the sawing rate in blocks 4 feet
thick is 25 to possibly 100 square feet an hour. A disadvantage of the
circular saw is its inability to make more than a single cut at once. When
slabs are to be sawed on both sides the block is returned to a starting
car and carefully aligned for a parallel cut. Both circular and gang saws
are used very widely.

An unusual granite-cutting machine, known as the "Chase" saw,
consists of a series of nine massive steel blades, about 20 inches wide
and M inch thick arranged in tandem, pivoted near the center and swing-
ing back and forth with an edgewise motion actuated by a crank and
pitman. Steel shot are used as abrasive. Granite blocks are mounted
on a traveling bed and joined with plaster of paris in exactly the same
way as for cutting by a circular saw. The machine can saw blocks with a
maximum thickness of about 5 feet, and cuts at a rate of about 2 inches a
minute in blocks 4 feet thick, or about 40 square feet an hour. Like
the circular saw it is limited to single cuts, but its operation is con-

162 THE STONE INDUSTRIES

tinuous. In so far as the writer is informed, only one such saw is now in
use.

Sawing of granite is costly and therefore employed only in preparing
the higher grades of ornamental or structural stone. Though expensive,
sawing has certain definite advantages. Thin slabs which could not be
shaped profitably in any other way are readily obtained. Furthermore,
the most attractive surface on some granites parallels the hard way,
and by ordinary methods of splitting with wedges it is difficult to obtain
blocks having their larger surfaces parallel to this direction, while
sawing may be done as readily in one direction as another.

An important advantage of sawing is conservation of stone. In
splitting with wedges irregularities are bound to occur, and much stone
is wasted in smoothing surfaces, while a saw removes little more than an
inch of material and leaves the surfaces smooth and straight. Such
smooth faces are advantageous in following processes, for sawed slabs
are smoothed with very little labor before polishing. Sawed blocks of
cut stone that have had no surface treatment other than sand blasting
are acceptable to many builders and architects.

Finishing the Surface. — A crude form of granite polishing was known
to the Egyptians, but the art apparently was lost until rediscovered by
granite workers at Aberdeen, Scotland, about 1820. Polished granite
is now used widely for monuments and ornamental building purposes; and
because of its hardness, crystalline character, variety of color, and trans-
parent grain it has superior beauty and endurance. Sawed slabs, or blocks
reduced to uniformity with surfacing machines, are carried through
several stages of treatment before a final polish is attained. The suc-
cessive steps are known in Vermont as "ironing," "emerying," "honing,"
and "buffing." Although different names may be applied in other
States the processes are essentially the same in all granite districts.

IRONING, — Surfaced or sawed blocks are placed in groups of 8 or 10
on a timber bed with their upper surfaces on an even plane. The
rectangular group of blocks is surrounded by a wooden box, with the
bottom a little lower than the surface of the rock. All cracks in the box
and between the blocks are filled with plaster of paris. A worker guides a
belt-driven revolving head over the blocks, and steel shot with water
coming between the rotating head and the stone gradually wear down the
surface. The rotary head, known as a "scroll," is a series of concentric
or spiral iron rings or segments of various patterns, some of which are
broken or notched. The patterns are designed to keep the abrasive
under the scroll as long as possible and to make it cut effectively. For
machines guided by hand scrolls may be 3 or 4 feet in diameter. The
process of thus wearing down a surface with steel shot is known locally
as "ironing." Two beds usually are provided within reach of each
machine, and, while stone on one is being smoothed, blocks are being

GRANITE 163

leveled and set in plaster on the other; thus the machine may be kept
in almost constant use.

EMERYiNG. — The next step, known as "emerying," produces a
smoother finish. It requires a lighter scroll and emery or more com-
monly, Carborundum powder, as abrasive. Three or four grades of
abrasive successively finer in grain size are employed, the coarser being
washed carefully from the surface before the next is added.

BUFFING. — For the final polishing process, generally known as "buff-
ing," a buffer head is operated in the same way as the scrolls. It consists
of a circular disk mounted with numerous folds of paper-mill felt. Putty
powder (extremely fine-grained tin oxide) is added, with a moderate
supply of water. If more than one surface is to be polished the block is
turned and reset in another bed. An experienced worker can completely
polish a bed in 1 day. Small surfaces, and designs in other than flat
surfaces are polished by hand methods or by small machines which will be
described later.

MODIFIED METHODS OF FINISHING SURFACES. — The brief descriptions
already given cover processes that have been long used, but certain
recent changes and improvements deserve mention. Automatic polishers
that require little or no hand work are being used more widely. On some
the rotating scroll is driven back and forth over the length of the bed or
block, its movement being automatically reversed with a trip set in any
desired position.

Another type of automatic polisher travels laterally across a bed
mounted directly on a large car. The car carrying the stone moves back-
ward and forward while the polishing wheel travels crosswise, both
motions being under control of an operator. Such mechanically operated
ironing wheels may weigh 3,000 pounds, and therefore cut very rapidly.
Ironing, emerying, and buffing follow in succession by changing the rotat-
ing heads and the abrasive. Starting with rough, unsurfaced quarry
blocks a final polish may be attained at a rate of about 15 square feet an
hour on one machine.

Much surface finishing is now done without setting the blocks in
plaster of paris. They are merely placed and leveled on a base block in
an enclosed area which collects the splash. A great deal of time is saved
thereby. When plaster beds are dispensed with, provision is made for
mechanical recovery and return to the surface of used coarser abrasive.
A typical mill is equipped with three machines, the first using coarse
silicon carbide, the second four successive grades of fine silicon carbide
or emery, and the third a buffer head. Automatic polishers are employed,
and blocks may be mounted on opposite sides of each machine for
alternate and practically continuous operation. It is claimed that such
equipment will polish about 350 square feet a day. To attain this

164 THE STONE INDUSTRIES

footage, however, sawed slabs only are used, a circumstance which
shortens the smoothing time materially, as it eliminates ironing.

SPECIAL SURFACE FINISHING. — Many blocks that can not conveniently
be placed beneath a regular buffer are polished with special machines con-
sisting of small buffer heads guided over the surface by hand and driven
by small electric motors mounted directly on movable frames. Small,
air-driven, portable polishing disks are used for narrow edges. Curved
or irregular surfaces are polished by hand.

Carborundum Machines. — Specially designed silicon carbide wheels
cut moldings and rabbitts, shape fluted columns, recess panels, and
handle similar processes. They must be operated carefully and with an
abundance of water. The granite block usually is mounted on a traveling
bed that carries it beneath the wheel, which cuts a groove about one-
eighth inch deep at each motion. Some wheel mountings may be reversed
to groove both the top and bottom of a block. On others the crosshead
carrying the arbor unit will swing through an angle of 90° to cut moldings
of any desired inclination. A "contour" machine is a special type
designed to follow a given pattern. The life of a wheel varies; with
fairly constant use one costing $7.50 will last about one day. Car-
borundum machines cut accurately, and provide a very smooth finish;
a single machine accomplishes in a given period very much more than a
cutter using hand tools.

Turning Lathes. — Ornamental granite in sound blocks absolutely free
from incipient seams is widely used for columns. The shaping, turning,
and polishing of columns are a distinct granite-cutting art. The block
first is roughed out to an approximately cylindrical form by drilling,
wedging, shaping with a bull sett, and dressing down with hand hammer
and chisel. Exceptionally, a cylindrical block of granite is cut by means
of a rotating drum fed with steel shot.

The rough cylinder is mounted in a lathe in which it rotates slowly.
One or more steel disks are mounted on axes inclined about 45° to the
axis of the column. The disk is not power-driven but turns freely as its
edge comes in contact with the rotating column. As the disk travels
slowly lengthwise to the column it chips off projections and gradually
works the surface to a uniform cylindrical shape. The column is then
ground smooth with steel shot, followed by emery or other abrasive, and
polished with putty powder on buffing pads held against it as it rotates.

One mill in Barre, Vt., speciaUzes in cutting columns. Large lathes
are provided for turning massive monoliths. Numerous small lathes
are employed for small columns, balusters, and spindles, as well as for
ornamental urns, vases, and flowerpots, which are used principally in
cemeteries. The dimensions and shapes are shown in drawings which for
smaller objects are full size. As turning proceeds, diameters are measured
with calipers, and contours are fitted to patterns. Square bases and

GRANITE 165

caps of columns are cut in the lathe with Carborundum wheels, the
lathe being locked from turning while each cut is in progress. Silicon
carbide wheels also cut grooves in cylindrical objects, the wheel and the
stone rotating at the same time. The turned column is placed in another
lathe for ironing, emerying, and buffing. An iron plate is fitted to
irregular contours, and an abrasive is fed under the plate by hand as the
column rotates. For straight surfaces a flat bar is used; for small,
curved surfaces a piece of iron pipe is held firmly against the rock and
moved back and forth while an abrasive mud is added. Very beautiful
polished objects are thus manufactured.

Surface Finishes. — Granite products have various types of surface
finish. For certain building and monumental uses a "rock-faced"
finish is preferred — that is, a rough broken surface like that obtained
when spalls are broken off with a sledge. Edges of rock-faced surfaces
usually are outlined with a pneumatic tool.

A "hammered" or "axed" finish is obtained by surfacing with a bush
hammer. It shows faint parallel ridges, and the surface is white or very
light. A "steeled" surface is obtained by "ironing" with steel shot. It
is intermediate in smoothness between hammered and polished, for it
shows faintly the color of the rock rather than the uniform white or light
gray of the hammered surface; thus, a steeled Barre granite is bluish.
A polished surface is the most ornamental, for it brings out the color of
each individual surface grain and shows all details of texture. It is also
easiest to clean. Polished granite is used widely for monuments and for
the lower courses, columns, and other prominent parts of large buildings.
A granite that shows a sharp contrast between polished and hammered
surfaces is preferred for monuments, because inscriptions stand out
prominently.

Arrangement of Mills. — In modern granite mills machines are
arranged in logical order, so that blocks travel by the shortest and most
convenient route until they arrive at the point of storage or shipment.
Overhead traveling cranes handle blocks expeditiously. Small cranes
are provided for quick handling of small blocks, while large, powerful,
though slower moving cranes, handle masses weighing up to 40 or 50
tons. The general arrangement and operation of cranes are similar to
those of limestone-finishing mills described in some detail in a previous
chapter. Mills are usually well lighted, heated, and ventilated and are
equipped with suction fans for removing granite dust from machines and
tools.

Storage and Shipment. — Products of granite mills are sold chiefly to
retail monument dealers or to builders and contractors. As large stocks
may accumulate, space must be provided for storage, and equipment
for handling and loading. Monuments and polished building stones are
crated carefully to protect them from damage during handling and

166 THE STONE INDUSTRIES

transportation, and usually stored under cover in such positions that they
may be readily located and conveniently loaded. Polished and carved
surfaces are protected with wrapping paper and sometimes with special
waterproof paper under the crating to guard against temporary stains.
Building granite ordinarily is stored in the open. Sometimes the stone
for an entire structure is cut before any is shipped, which requires careful
planning and arrangement so that blocks may be shipped in the order in
which they are to be placed. On other contracts rock may be loaded for
shipment practically as fast as cut. As granite is a heavy product all
unnecessary handling is avoided.

MARKET RANGE

Finished monuments from the mills of Barre, Vt., are the most widely
distributed in all granites and are marketed in practically every State.
The granites of Quincy, Mass., also are widely distributed. Granite
monuments from St. Cloud, Minn., and from Wisconsin are marketed
largely in the Middle West, although they are used to some extent in
more distant States. The "black granites" of Pennsylvania and New
England are sold chiefly in New York City. Building granites produced
principally near the Atlantic seacoast of New England, and in Penn-
sylvania, North Carolina, Georgia, and California are marketed chiefly
in the larger cities where they are used for entire structures or for
base courses and trim in residences, office buildings, stores, banks,
churches, schools, and other public buildings. An important application
is in bridge construction. For this use it may be shipped for long
distances; for example, Georgia and North CaroUna stone has been used
in large bridges in Philadelphia and New York.

IMPORTS, EXPORTS, AND TARIFFS

About 60 per cent of the imports of unmanufactured monumental
granite is obtained from Sweden. The Swedish granites are chiefly dark
varieties, the so-called black granites. Red granite from Finland is
second in importance. Imports of monumental base stock and building
granite come chiefly from Canada.

Imported manufactured granite consists largely of monument dies
with polished surfaces. The chief imports, which come from Germany,
consist of dies manufactured from Swedish granite. Finland is second in
importance for manufactured as well as for unmanufactured granite.
Imported manufactured granite is purchased for the most part by whole-
sale dealers in Ohio, for sale to retail monument dealers west of the
Alleghenies.

According to tariff classification granite exports are combined with
exports of a number of other commodities and therefore cannot be shown
separately, but the amount is small.

GRANITE 167

According to the Tariff Act of 1930 granite suitable for use as monu-
mental, paving, or building stone, not specially provided for, hewn,
dressed, pointed, pitched, lined or polished, or otherwise manufactured
bears a duty of 60 per centum ad valorem; on unmanufactured granite
the duty is 25 cents a cubic foot.

PRICES

Buifding granite is sold principally on lump-sum contracts. When
sold on smaller contracts random blocks without cutting or carving are
quoted at prices ranging from $1.40 to $2.25 a cubic foot at points of
consumption. Unmanufactured monumental granite is $3 to $4.50 a
cubic foot f.o.b. quarry.

Bibliography

AxjBURY, Lewis E. The Structural and Industrial Materials of California. Cali-
fornia State Min. Bur. Bull. 38, 1906, pp. 23-61.

Bowles, Oliver. Structural and Ornamental Stones of Minnesota. U. S. Geol.
Survey Bull. 663, 1918, 225 pp.

Bowles, Oliver, and Hatmaker, Paul. Trends in the Production and Uses of
Granite as Dimension Stone. Rept. of Investigations 3065, U. S. Bur. of Mines.
1931, 21 pp.

Buckley, E. R. Building and Ornamental Stones of Wisconsin. Wisconsin Geol.
and Nat. Hist. Survey Bull. 4, 1898, 544 pp.

Buckley, E. R., and Buehler, H. A. The Quarrying Industry of Missouri. Mis-
souri Bur. Geol. and Mines, vol. 2, 2d ser., 1904, pp. 60-85.

Coons, A. T. Chapters on Stone. Mineral Resources of the United States, pub-
lished annually by the U. S. Bur. of Mines. (U. S. Geol. Survey prior to 1924,
Minerals Yearbook since 1931.)

Dale, T. Nelson. The Commercial Granites of New England. U. S. Geol. Survey
Bull. 738, 1923, 488 pp.

Eckel, E. C. Building Stones and Clays. John Wiley & Sons, Inc., New York,
1912, pp. 32-68.

Federal Board for Vocational Education. Granite Cutting, An Analysis of the
Granite Cutter's Trade. Bull. 137, 1929, 251 pp.

Merrill, G. P., and Matthews, E. B. The Building and Decorative Stones of
Maryland. Maryland Geol. Survey, vol. 2, pt. 2, 1898, pp. 136-168.

Nash, J. P. Texas Granites. Univ. of Texas Bull. 1725, 1917, 8 pp.

Newland, D. H. The Quarry Materials of New York; Granite, Gneiss, Trap, and
Marble. New York State Museum Bull. 181, 1916, pp. 58-175.

Richardson, C. H. Building Stones and Clays. Syracuse Univ. Book Store,
Syracuse, N. Y., 1917, pp. 38-133.

U. S. Tariff Commission. Granite. Rept. to the President of the United States,
1929, 72 pp.

Watson, T. L. A PreUminary Report on a Part of the Granites and Gneisses of
Georgia. Georgia Geol. Survey Bull. 9-A, 1902, 367 pp.

Granites of the Southeastern Atlantic States. U. S. Geol. Survey Bull.

426, 1910, 282 pp.

Watson, T. L., and Laney, F. B. The Building and Ornamental Stones of North
Carolina. North Carolina Geol. Survey Bull. 2, 1906, 283 pp.

CHAPTER IX

MARBLE

HISTORY

Marble working is an ancient art. Because of its attractive crystalline
form marble was one of the first stones to be used for carving and for
structural purposes. Biblical references to its use in Solomon's Temple
at Jerusalem and the palace of Shushan indicate that it was well-known
for building and decoration more than 1,000 years before the Christian
era. Parian marble was used by the early Greek sculptors in such
famous statues as Venus de Medici, and the Parthenon was built of the
renowned Pentelic marble. Carrara, Italy, has long been a center of
marble production, as well as of art and architecture. We are, indeed,
indebted to the enduring qualities of this stone for preservation of many
magnificant and inspiring examples of sculpture and structural design
that might otherwise have been lost. Numerous invaluable records
inscribed on marble slabs have added to our wealth of ancient history.

DEFINITION

In its geologic sense the term "marble" is applied to rocks consisting
of crystallized grains of calcite, dolomite, or a mixture of the two. Marble
has the same chemical composition as limestone or dolomite, the chief
difference being that the component particles of calcium or magnesium
carbonates in limestone are granular and noncrystalline. It is regarded
as a metamorphic rock resulting from the recrystallization of limestone.

In its commercial sense, the term has a much wider application. As
susceptibility to polish is one of its chief commercial assets, all calcareous
rocks capable of taking a polish are classed as marbles. Furthermore,
serpentine rocks, if attractive and capable of taking a good polish, are so
classed, even though containing little calcium or magnesium carbonates,
as they are commercial substitutes for true marbles.

COMPOSITION

Aside from serpentine and other extraordinary varieties, marble
consists almost entirely of calcium or magnesium carbonates. A calcite
marble may include 95 to almost 100 per cent calcium carbonate. If
impurities are disregarded a dolomite marble contains approximately 54
per cent calcium carbonate and 46 per cent magnesium carbonate. Those
comprising mixtures of calcite and dolomite may have compositions any-

168

MARBLE 169

where between these two extremes. Varying percentages of impurities
are present in practically all marbles. The more common impurities are
silica (Si02), either as free quartz or combined in silicates; iron oxides,
such as hematite (Fe203) and limonite (2Fe203.3H20) ; manganese oxide
(MnO); alumina (AI2O3), in the form of aluminum silicates; and sulphur,
usually as pyrite (FeS2). Small quantities of organic matter may be
present ; in some marbles it has been converted into graphite. Impurities
occur as common minerals, and their presence gives to colored marble the
veins and markings that sometimes adapt it to decorative uses. The
more common mineral impurities are quartz or some other form of free
silica, such as chert or flint, hematite, limonite, graphite, mica, chlorite,
tremolite, woUastonite, diopside, hornblende, tourmaline, and pyrite.
In the marbles of southern Ontario, Parks^* notes the presence of 37
minerals that have been formed by metamorphic processes acting on
the impurities of the original limestone. Impurities in their relation to
use are discussed more fully on pages 175 to 177.

ORIGIN AND VARIETIES

Marbles may be classed in three groups.

The first group, which includes by far the largest proportion, com-
prises those resulting from recrystallization of limestone. Most of them
are highly crystalline and are usually white, though gray, black, or other
markings may be present. A preponderance of the Alabama, Georgia,
Vermont, Massachusetts, Connecticut, and southeastern New York
marbles are -of this type. The original rocks were formed in the sea,
mainly as accumulations of the calcareous remains of marine organisms,
which were consolidated to form coherent rocks termed "limestone."
The origin of limestone is described more fully in the chapter on limestone.
Heat and pressure, usually accompanied by extreme deformation of the
beds, resulted in the highly crystalline condition most commercial
marbles exhibit. Recrystallization as a result of igneous intrusion has
been noted. Fossiliferous or subcrystalline marbles have been subjected
to less extreme metamorphism, and in many instances the original fossils
remain almost intact. They have sufficiently close texture to take a
good polish and at the same time show attractive color effects. Water
probably has assisted greatly in their recrystallization. In fact, some
marbles seem to have been altered from limestones chiefly by circulating
water, for they show no evidence of deformation or extreme pressure, nor
are they near igneous intrusions.

The second group comprises the onyx marbles. These consist
essentially of calcium carbonate and are purely chemical deposits that
have not resulted from metamorphism of preexisting limestone beds.

^' Parks, W. A., Report on the Building and Ornamental Stones of Canada.
Canada Dept. of Mines, Mines Branch, vol. 1, no. 100, 1912, p. 307.

170 THE STONE INDUSTRIES

Such calcareous chemical deposits are of two types. One, which is
regarded as a product of precipitation from hot springs, is termed traver-
tine. As most travertines are porous and can not take a fine polish,
they are classed with limestones rather than with marbles. The other
type, true onyx marble, usually is regarded as a deposit from cold-water
solutions, commonly in limestone caves, hence the name "cave onyx" is
sometimes applied to it. Impurities, such as iron and manganese oxides,
may be present in varying amounts in successive layers of this marble,
and thus beautiful banding may result. This type is commonly known
as Mexican onyx because very fine deposits have been found in Mexico.
Many onyx marbles are semitranslucent.

The third group includes the verde antiques. The name is applied to
marbles of prevailing green color, consisting chiefly of serpentine, a
hydrous magnesium silicate. They are highly decorative stones the
green color being interspersed at times with streaks or veins of red and
white. In no respect are they comparable with true marbles in either
composition or origin. Serpentine is in general derived from the altera-
tion of basic igneous rocks, such as the peridotites which are rich in olivine
and pyroxene, or from magnesium silicate rocks formed by metamorphism
of impure dolomitic limestone. The process is accompanied by hydra-
tion, with an addition of 13 to 14 per cent of water. The movement
occasioned by the swelling that results probably accounts for most of the
unsoundness common to verde antique.

PHYSICAL PROPERTIES

Hardness. — As defined on a previous page, hardness is a measure
of the resistance the surface of a substance offers to abrasion. As given
in Moh's scale the hardness of calcite is 3 and dolomite 3.5 to 4, whereas
window glass is about 6. Marbles are harder than most limestones, for
while they may consist of the same mineral — calcite — grains of limestone
usually are cemented together less firmly, and hardness of a granular
rock is measured by the degree of cohesion between grains rather than by
the actual hardness of the mineral. The presence of such impurities as
flint or silicate minerals may increase the hardness of a marble very
greatly. Hardness of the mass as a whole is an indication of "work-
ability" and is an important property, as the cost of quarrying marbles
that are worked slowly by tools is much higher than that of those easily
worked. Although the cost of quarrying hard marble may be high,
hardness is a desirable property if the material is to be exposed to abrasion.

High resistance to abrasion and uniform hardness are desirable
qualities in marbles to be used for sills, steps, or floor tile, all of which are
exposed to the friction of feet of pedestrians. In constructing floor
patterns of different marbles it is important that they be equally resistant

MARBLE 171

to abrasion, otherwise the floor eventually will become uneven. This
condition may be observed in the Union Station at Washington, D, C,
where tiles of relatively pure calcite marble are worn down in places
nearly half an inch lower than the smaller squares of harder, colored,
siliceous marble.

Specific Gravity and Weight per Cubic Foot. — The specific gravity of a
substance is its weight compared with that of an equal volume of water.
The specific gravity of calcite is 2.7 and that of dolomite about 2.9.
Consequently, dolomite marbles are heavier than calcite marbles. It is
found that the actual weight per cubic foot of a block differs more or less
from its theoretical weight calculated from the specific gravity of the
constituent minerals. A porous rock of given volume will be lighter than
an equal volume of similar nonporous material.

The pore space in most marbles is so small that the actual weight
does not differ greatly from that calculated from specific gravity. Marbles
range from 165 to 180 pounds per cubic foot in actual weight.

Solubility. — The solubility of marble deserves careful consideration if
its use for exterior purposes is contemplated, because all stones dissolve
slowly or disintegrate when exposed to atmospheric agencies. Usually
the rate of solution is extremely slow, but it may be rapid enough under
certain conditions to impair the value of stone for building. The rate of
solution varies in different marbles, depending on chemical composition,
texture, and porosity. Surface waters which contain certain dissolved
gases, such as carbon dioxide, dissolve the carbonates to a limited degree.
Near large cities various acids from smoke are taken up by rain and
increase its power of solution. If a stone is permeable it usually dissolves
more rapidly than if impervious. Calcite dissolves more rapidly than
dolomite under the same conditions if the texture of each is similar, but
the tendency for dolomite to occur with granular texture often reverses
the order of their solubility.

Color. — The color of a marble, one of its most important physical
properties, is governed by the nature of the constituents. Marbles con-
sisting of pure calcite or dolomite are white, whereas green is the prevail-
ing color of verde antique. Variations from the whiteness of a pure marble
are due to admixtures of foreign substances. Such impurities may be
distributed uniformly and thus give uniform coloration or they may be
present in bands or streaks, giving clouded or otherwise nonuniform
colors. Very beautiful banded effects are obtained by sawing veined
marbles in certain directions.

The causes of some colors in marbles are easily determined. Black
and grayish shades are attributed to carbonaceous matter, which is
usually present as fine scales of graphite ; red, pink, or reddish brown are
due mainly to the presence of manganese oxides or to hematite; yellow-
brown, yellow, or cream are caused by minute grains of limonite, a

172 THE STONE INDUSTRIES

hydrous oxide of iron. Other colors, such as the bluish tint found in
some beds of white marble, are difficult to explain.

Highly colored marbles are usually those that have been brecciated
or fractured, subsequent consolidation being accompanied by infiltration
of coloring material from surrounding soil and rocks. They are mostly of
foreign origin.

For certain purposes, particularly for monuments on which inscrip-
tions are cut, marble which presents a distinct contrast between chiseled
and polished surfaces is desirable. A chiseled surface is opaque and
somewhat granular and reflects rather than absorbs light ; hence it tends to
appear white or light-colored, even if the stone is dark. When a face is
polished the reflecting surfaces are removed, and light is permitted to
enter the crystals and be absorbed, which causes the polished surface to
appear relatively dark. The contrast usually is more pronounced in
colored and less marked in the white marbles.

Each bed in a deposit exhibits more or less constancy of color; there-
fore, desirable uniformity in color ordinarily can be maintained by
working each bed separately. If the texture or color of marble in a
deposit varies, care is taken to quarry in such manner as will tend to
produce material that may be closely classified. Some variations in
color, though slight, may detract immensely from the market value.
Lenses and bands of bluish material may pass irregularly through the
white, occasioning excessive waste or necessitating classification in a
lower grade.

Colors may be permanent or may change after exposure to sunlight or
weather, the more highly colored marbles being most subject to such
changes. Severity of climate is an important factor in these changes.
Permanence of color is highly desirable. Most high-grade American
marbles show very slight color alteration even after long periods. A
soiled surface must not, of course, be confused with color changes.

Translucence. — Translucence is a measure of the capacity of marbles
for transmitting light. The more translucent varieties, if fine-grained,
are best-adapted for novelties or other ornamental purposes. Some
marbles look waxy, and this property seems to be related to translucence.
The depth to which light will penetrate the best statuary marbles ranges
from }yi to 13-^ inches. Certain beds in many marble deposits of the
United States are exceptionally translucent. The beautiful so-called
"transparencies" in the roof of the Lincoln Memorial at Washington,
D. C. are translucent slabs of clouded and veined Alabama marble.
Certain modes of artificial treatment are known to increase translucence,
but usually the effects of such treatment are far less permanent than the
material itself and consequently are not to be recommended.

Texture. — Grains of calcite and dolomite that make up a marble mass
are crystalline and have a definite cleavage, showing bright reflecting

MARBLE 173

faces on a broken surface. Usually the cleavages appear about equally-
prominent in every direction. In some marbles, however, the grains
are elongated in one direction by the folding or plication of beds. Most
marbles consist of a single mineral, and therefore have a homogeneity
that is favorable for resistance to weathering because of uniform expansion
and contraction with temperature changes. The texture of a marble
thus depends on the form, size, uniformity, and arrangement of its grains,
and on the nature and size of grains of accessory minerals.

The size of grain is commonly described as fine, medium, or coarse.
Such terms are indefinite and may have quite different meanings, the
interpretation depending upon the range of texture experienced by the
observer. To place texture upon an absolute basis Dale graded
the marbles of Vermont into six classes, based upon average grain
diameter, as follows: Extra fine, 0.06 millimeter; very fine, 0.10; fine, 0.12;
medium, 0.15; coarse, 0.24; and extra coarse, 0.50.

Rift or Grain. — While the terms "rift" and "grain" have distinctive
meanings as applied to sandstone and granite, in connection with marble
they are used synonymously for the direction of easiest splitting. The
rift usually parallels the bedding, and it is probably due to elongation
of grain caused by pressure. It may be emphasized by the presence of
platy or fibrous minerals, such as scales of mica or graphite or needles of
actinolite. These usually occupy positions with their long axes parallel
to the direction of grain elongation and thus increase the tendency to
split in that direction. Quarrymen find it advantageous to follow the
direction of easy splitting, for thus wedges may be placed much farther
apart than where no rift exists.

Porosity. — Porosity is the volume of pore space expressed as a
percentage of the total volume of a rock mass. The pore space of high-
grade marbles is usually very small, ranging from 0.0002 to 0.5 per cent.
A fine-grained marble may have more pore space than one of coarser
texture, but the opposite is more often true. Low porosity in exterior
marble is desirable, as pores permit infiltration of water, which may dis-
solve or discolor the stone or cause disintegration by freezing. Porous
stones also collect soot or particles of soil and therefore are not
satisfactory when exposed to excessive smoke or dust. Practically all
marbles recommended for exterior use have very low porosity.

Strength. — The strength of marble is the measure of its capacity to
resist stresses of various kinds. It depends partly on the rift, on the
cleavage and hardness of the grains, and partly on the state of
aggregation, including degree of cohesion, interlocking of grains, and
nature of cementing material if such is present. Compressive, transverse,
tensional or cohesive, and shearing strength all affect use, but compres-
sive strength is the quality most commonly tested.

174 THE STONE INDUSTRIES

Although strength alone is not a sure criterion of durability, knowledge
of the capability of any stone to withstand stresses of various kinds has
great value if the material is to be used for purposes involving extra-
ordinary strains. Practically all commercial grades of sound white
marbles can support many times the weight of structures in which they
are ordinarily used, though some brecciated and veined marbles are too
weak to sustain heavy loads with perfect safety. As a rule, marble is
stronger across the bedding plane than parallel to it. Compressive
strength has no significance in judging the quality of cemetery memorials.

Transverse strength indicates the suitability of a marble for door or
window caps or for bridging material that must bear heavy loads. Break-
age of caps, however, must not always be attributed to weakness in the
material employed, as unequal settling or improper laying may be the
chief cause.

When subjected to crushing strain rocks can be compressed appreci-
ably before rupture occurs. A measure of this compressibility in terms
of the load is what is known as the modulus of elasticity. The compressi-
bility of marble is so small that it has little significance, except possibly
in calculating the effect of a very heavy superstructure on a masonry
arch or in proportioning abutments and piers of massive bridges, A high
modulus of elasticity is desirable in marble subjected to minor stresses
and strains due to setthng of buildings.

JOINTING OR UNSOUNDNESS

Meaning of Unsoundness. — The term "unsoundness" refers to all
cracks or lines of weakness other than bedding planes that cause marble
to break before or during manufacture. The various types are known
locally as "joints," "headers," "cutters," "hairlines," "slicks," "seams,"
"slick seams," "dry seams," or "dries," and "cracks." The term
"reed" is applied to a weakness that parallels the bedding.

Nature and Importance of Joints. — Most joints, as they appear in
marble deposits, are straight and uniform, though some may be curved or
irregular. Some are open and conspicuous and others so obscure that
they can be recognized only by long and constant practice on the part of
those skilled in their detection. The spacing of joints is variable. They
tend to occur in groups of closely spaced fractures, separated by masses
which contain few joints. In certain Vermont quarries such closely
spaced groups are termed "fish-backs." In some deposits joints may be
10 to 30 feet apart, in others, separated by only a few inches. Needless
to say, wide spacing adds greatly to the commercial value of a deposit.

Origin of Joints. — Authorities generally agree that joints are caused
by strains in rock masses. As pointed out in the chapter on granite, a
compressive force in one direction will develop two systems of joints at
right angles to each other, and at angles of 45° to the line of pressure.

MARBLE 175

Torsional forces or earthquake shocks alone or in conjunction with other
forces may have a similar effect. Both direction and spacing, as observed
at the surface, may persist with remarkable uniformity at depths of 100
feet or more.

Therefore, according to the theory noted in the paragraph immedi-
ately preceding, which is supported by results of many observations,
joints tend to occur in regular systems. Two systems approximately at
right angles to each other are not uncommon. Occasionally a third or
fourth system may appear. Exceptionally no well-defined systems can be
recognized. The systematic arrangement is recognized by most quarry-
men and is an important factor in the economy of marble working.
Greater loss results from quarrying without regard for unsoundness than
from any other cause. Operators may augment the proportion of sound
stock by making careful study and detailed diagrams of all visible
unsoundness and by quarrying in conformity with it. That is, walls
should be made to parallel the major joint systems, and all subsequent
cuts so arranged in spacing and direction that seams will intersect blocks
as little as possible. Blocks intersected by oblique joints are almost
useless.

Unsoundness in Verde Antique. — Joints in serpentine marble, or
what commonly is called "verde antique," usually are rather abundant
and extremely irregular. They are probably caused chiefly by expansion
or swelling due to hydration as the serpentine is formed. Consequently,
joints are usually less systematic in this variety than in white marbles,
and large, sound blocks are more difficult to obtain. Occasionally the
cracks are recemented by crystalline calcite, which produces an attractive
white veining on a green background. The so-called brecciated marbles
are composed of many irregular and usually angular fragments that have
been cemented by chemical precipitation of calcium carbonate.

Glass Seams. — Joints that have been recemented in nature are
sometimes termed "glass seams." They may be strong enough to
permit sawing the marble even into thin stock, but such seams are usually
planes of weakness. The filling is generally calcite, though occasionally
silica in the form of quartz, flint, or chert. A siliceous filling is least
desirable because its extreme hardness makes sawing and polishing
difficult, and because its surface is nonuniform. In any case, a glass
seam usually appears as a conspicuous line which can be regarded only as a
blemish when present in otherwise uniform marble.

CHIEF IMPURITIES OF MARBLE

Iron Sulphides. — The chief iron sulphides in marble are pyrite and
marcasite, which have the same chemical composition (expressed by
the formula FeS2), though they differ in crystal form. In many marble

176 THE STONE INDUSTRIES

deposits they are accessory minerals, pyrite being the more common,
and may appear as scattered crystals of variable size or form prominent
bands and masses. Decomposition of the sulphides may result in undesir-
able discolorations, consisting of iron oxides.

Most authors who have discussed impurities in building stone have
stated unreservedly that pyrite is injurious when the stone is used for
exterior work. This statement is not always true, however. Although
the sulphides in some marbles decompose and form undesirable dis-
colorations in a few months, those in marble from other deposits may
withstand many years of weathering and show no appreciable change.
Some American marbles containing pyrite have been exposed to the
weather for more than 100 years without noticeable staining.

Pyrite is usually more stable than marcasite. Solid crystals of either
mineral usually decompose slowly, though finely divided granular or
porous forms of either alter rapidly. Mixtures of pyrite and marcasite
decompose more readily than the pure minerals. A fair conception of
the probable stability of the sulphides in a marble may be gained by
making observations and tests. The most reliable information is obtain-
able by observing stain effects on structures of sulphide-bearing marble
or on weathered outcrops of the deposit from which it was obtained.
Iron sulphide is not necessarily injurious in marble but should be avoided
carefully in the selection of stone for exterior uses where discoloration is
undesirable. In some instances, however, discoloration by weathering
may not be detrimental, for such color changes may blend with the normal
mellowing and ageing of the stone.

Marble containing pyrite may be used to advantage for interior
structural or ornamental purposes, as bands and patches of the iron
sulphide minerals produce beautiful effects on polished surfaces. Pyrite
crystals are very hard, however, and may injure tools used in cutting.

Silica. — Knots or bands of silica derived from skeletal remains of
organisms may be original constituents of marble. Silica may also be
introduced into a marble bed at a later stage in the history of the deposit.
Water that percolates through fissures in the mass may contain small
quantities of silica in solution, which may be precipitated in cracks and
cavities. Silica in this form tends to follow unsoundness and may even
effectually seal fractures. The presence of silica usually detracts from
the appearance of marble. As a rule, the flinty or cherty mass differs
from the marble in color or texture and constitutes a blemish comparable
to that produced by a knot in an otherwise uniform stick of timber.
Occasionally, however, flinty masses are the basis for distinctive decora-
tive markings that are an asset to the stone. Silica is at least twice as
hard as ordinary marble, consequently, it greatly retards channeling,
drilling, or sawing and injures tools, especially wire saws. A flint ball
may divert a saw to one side or may greatly reduce the rate of cutting.

MARBLE 177

Moreover, uniformity of finish under a buffer is difficult to obtain on the
surface of a flinty marble on account of its unequal hardness.

Silicated Marbles. — Silicated marbles contain pyroxenes, amphiboles,
mica, chlorite, or other silicates which are commonly formed by alteration
of interbedded impurities. Marbles may therefore contain bands of these
minerals, which sometimes remain conformable with the original bedding.
In such form they are not serious imperfections and may even facilitate
quarrying. However, silicate impurities, especially mica and chlorite,
may be scattered throughout the mass in dark bands and patches which
generally detract from the market value of the stone although at times
they may be adapted to ornamental use.

Dolomitic marbles may contain tremolite, a silicate of calcium and
magnesium. The mineral generally occurs in the form of white crystals
with a silky luster and a characteristic diamond-shaped cross section.
They may be microscopic in size or may attain a length of 2 inches, and
are much harder than marble. Wollastonite, diopside, olivine, and
tourmaline are other common silicates present in marbles.

Dolomite in Marble. — Marble composed of alternating masses of
dolomite and calcite is undesirable. When dolomite is present in lenses
or bands, the resulting unequal weathering will produce a nonuniform
surface. Differences in texture, color, or susceptibility to polish of the
two minerals are also probable. Although pure dolomite, or intimate
mixtures of dolomite and calcite, is not to be regarded as an inferior
type of marble, heterogeneous mixtures in the form of lenses, knots, or
bands are undesirable for the reasons given.

GEOLOGIC INTERPRETATIONS

Intimate knowledge of the geology of marble deposits is a practical
necessity for intelligent quarry development. Beds of high quality must
be followed, and this demands an understanding of their stratigraphy,
including folding and faulting. The origin and occurrence of imperfec-
tions should be known. Operations also depend upon rock structures,
such as joints and dikes.

The quality of a marble tends to be fairly constant throughout a
given bed over wide areas. An adjoining bed, even though only a few
feet away, may have been deposited much later or earlier and under
vastly different conditions. Therefore, the greatest changes in quality
and character of rock are found in passing from one bed to another.
To obtain high quality and uniformity in the product the bedding must be
followed closely. Each bed generally is designated by a particular name,
and quarrymen usually are so familiar with characteristics of successive
strata that they can assign a block in a stock pile to its proper bed by
visual examination. This intimate knowledge of stratigraphy is exceed-
ingly practical in recognizing desirable beds in new openings made along

178 THE STONE INDUSTRIES

the strike or in outcrops where beds reappear at the surface through
folding or faulting. Certain beds may be traced for many miles and may
maintain remarkable uniformity in quality and thickness. They may,
however, narrow, widen, or disappear entirely, and the quality may
change.

USES

Marble is used mainly for buildings and monuments, interior decora-
tion, statuary, and novelties.

In exterior building marbles qualities of endurance rank equally in
importance with appearance. For such outdoor uses, therefore, marbles
should be strong, uniform, close-grained (though not necessarily fine-
grained), reasonably nonabsorptive, and free from impurities that may
stain or corrode the surface. While uniformity in color was once desir-
able, the present tendency is toward blending of mixed colors.

For interior decoration, appearance is the prime factor determining
value. Both pure white and variously colored marbles are applied to the
various uses, including floors, steps, baseboards, columns, balusters, wall
panels, wainscoting, and arches. That used for floors and stair treads
should be reasonably resistant to abrasion. Brecciated marbles, most of
which are imported, are widely used for columns and wainscoting.
Verde antique is popular for interior decorative effects. It is used some-
times as an exterior ornamental stone as, for example, on banks and store
fronts. Onyx marble is popular for interior decoration, as it has a wax-
like appearance and attractive banding. Interior marble is used in
various minor ways, such as for table tops, lavatory fittings, and sanitary
work generally.

Statuary marble is the most valuable variety quarried. It must be
piire white, uniform and usually fine-grained in texture, and somewhat
translucent, and must have marked adaptability for carving. Numerous
statuary and decorative marbles from American quarries are now on the
market, each having its own particular trade name.

All the more ornamental types are used for novelties. A favorite
use of onyx is for the manufacture of gear-shift balls. Onyx, verde
antique, and true marbles are manufactured into inkwells, lamp bases,
smoking sets, clock cases, paperweights, and various other gift-shop
novelties.

Waste marble is used as crushed stone, terrazzo, stucco, and riprap,
for lime, for fluxing, and for various chemical uses covered in a later
chapter on limestone. Waste blocks are also cut into convenient sizes
for ashlar used in house construction.

DISTRIBUTION OF DEPOSITS

As recrystallization, the outstanding characteristic of marble, is
promoted chiefly by heat and pressure acting on the original limestone,

MARBLE

179

most marbles are confined to areas of extreme folding or igneous intrusion,
hence, occur chiefly in mountainous regions. The important marble
belts of the United States are in the Appalachian region of the Eastern
States and in the Rocky Mountain and Coast Ranges of the West.
Deposits also occur in several Central States and in Alaska.

The Appalachian belt, which is the most productive, follows a com-
paratively narrow, well-defined course as shown in figure 29. Beginning
at the Canadian border in northern Vermont it extends due south
through western Massachusetts and Connecticut and eastern New York
to within a short distance of New York City. No marble of consequence

Fig. 29. — Map showing marble deposits of eastern United States. (Prepared by H. Herbert

Hughes.)

occurs in New Jersey, except in the extreme west, but the belt reappears
prominently in southern Pennsylvania and extends southwestward
through Maryland, Virginia. North Carolina, Tennessee, Georgia, and
Alabama.

Marbles of the Central States occur in isolated localities, principally
Minnesota, Missouri, and Texas. For the most part, recrystallization
has been accompanied by very little, if any, deformation of beds.

Various types of marbles are found in the Rocky Mountain and
Pacific Coast States (in parts of California, Nevada, Montana, and
Colorado, with more restricted areas in Idaho, southwestern Oregon, and
northeastern Washington) but many are too inaccessible to have com-
mercial importance at this time.

180

THE STONE INDUSTRIES

PRODUCTION

The volume in cubic feet and value of marble sold in the United
States over a period of years are shown in the following table by uses:

Marble Sold by Producers in the United States, 1924-1937, by Uses

Building stone

„*„1 „4

Total

Year

Exterior

Interior

Cubic
feet

Value

Cubic
feet

Value

Cubic
feet

Value

Cubic
feet

Value

1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937

852,940

1,145,690

1,123,990

850,470

1,019,490

924,420

772,920

594,710

863 , 690

760,420

190,060

150,560

373,520

284,500

$2,621,088

3 , 559 , 686

3,350,434

2,826,079

3,146,202

3,849,510

2,685,924

2,986,901

2,213,673

2,396,571

523,033

494,097

1,701,864

938,570

1,753,240

1,719,610

1,743,950

1,973,320

2,005,150

1,854,380

1,698,180

1,066,640

818,160

583 , 890

309,950

217,890

398,440

447,200

$6,178,131
6,040,425
6,069,505
7,913,149
8,963,125
8,276,206
6,390,107
4,855,595
3,413,929
2,481,167
1,196,423
1,212,173
2,079,010
2,397,975

1,230,450

1,176,090

1,095,220

1,127,480

1,031,050

1,065,760

879,270

637,830

432,590

426,300

464,910

300,370

374,520

360,580

$3,858,190
,3,598,907
4,047,857
4,097,249
3,749,269
3,885,481
3,263,383
2,177,656
1 , 669 , 689
1,358,770
1,475,426
1,521,681
1,751,947
1,798,176

3,836,630
4,041,390
3,963,160
3,951,270
4,055,690
3,844,560
3,350,370
2,299,180
2,114,440
1,770,610
964,920
668 , 820
1,146,480
1 , 092 , 280

$12,657,409

13,199,018

13,467,796

14,836,477

15,858,596

16,011,197

12,339,414

10,020,152

7,297,291

6,236,508

3,194,882

3,227,951

5,532,821

5,134,721

Marble Sold by Producers in the United States, 1929, by States and Uses

Building and monu-
mental (rough and
finished)

Other uses

Total

State

Cubic feet

Value

Short
tons

Value

Short
tons
(approx-
imate)

Value

Alabama

California

Georgia

Massachusetts ....

Missouri

New York

Tennessee

Vermont

Other States*

52,900

14,260

676,190

19,720

477,010

51,220

1,312,180

1,185,100

55,980

$ 381,781

71,259

3,739,825

97,910

927,530

129,202

5,678,596

4,763,471

221,623

36,400
1,570
26,300
2,510
15,900
44,160
58,950
29,350
14,490

S 61,738

9,575

37,450

3,542

4,941

187,760

60,408

35,242

133,459

40,900

2,780

82,920

4,180

55,420

48,640

169,630

129,940

19,250

$ 443,519

80,834

3,777,275

101,452

932,471

316,962

5,739,004

4,798,713

355,082

3,844,560

$16,011,197

229,630

$534,115

553,660

$16,545,312

* Alaska, Arizona, Arkansas, Colorado, Idaho, Maryland, Montana, New Jersey, North Carolina,
Utah, Virginia, and Washington.

MARBLE 181

The eight leading States, in order of production value in 1929, were
Tennessee, Vermont, Georgia, Missouri, Alabama, New York, Massa-
chusetts, and California. The preceding table, compiled by the Bureau of
Mines, shows the total marble production during 1929 by States. These
figures are given in preference to those of later years, when conditions
were more disturbed.

In 1929, 111,580 cubic feet of verde antique (serpentine marble),
valued at $842,058, was sold in the United States; in 1930, 98,490 cubic
feet, valued at $695,131; in 1931, 39,150 cubic feet, valued at $218,098;
and in 1937, 16,300 cubic feet, valued at $145,136.

INDUSTRY BY STATES

Occurrences of marble in the United States are described in the
following pages by States in order of their production value in 1929, as
that year was probably more nearly normal than the three succeeding
years. Descriptions are confined chiefly to deposits in which quarries
have been recently in operation, minor attention being given to unworked
areas or abandoned quarries.

Tennessee.-* — As the preceding table indicates, in 1929 Tennessee
produced 1,312,180 cubic feet of building and monumental marble, valued
at $5,678,596, or about 35.5 per cent of the total value of marble produced
in the country. Production in 1930 was 1,019,300 cubic feet, valued at
$3,355,673; in 1931, 525,900 cubic feet, valued at $2,407,878; and in 1937,
267,370 cubic feet, valued at $1,384,961.

General Distribution. — The widely known marbles of east Tennessee
occur in rocks of Palaeozoic age in what is known as the Holston member
of the Chickamauga formation. The latter formation is of wide extent
and consists chiefly of limestone. The Holston beds are confined to the
Tennessee River Valley and outcrop in a series of nearly parallel bands.
The area is 12 to 16 miles wide and over 125 miles long. Marbles of
commercial quality occur in many places, and the supply is practically
inexhaustible. Two important railway lines traverse the area — the
Southern Railway, which extends throughout its length, and the Louis-
ville & Nashville Railway, which crosses it.

Tennessee marble was used locally for tombstones in very early days ;
but the history of production as an industry dates from 1838, when the
United States Government opened a quarry in Hawkins County to
provide interior marble for the Capitol at Washington. During ensuing
years other quarries were opened until an industry of great magnitude was
developed.

^^ Data on Tennessee marble deposits have been compiled chiefly from Tennessee
Geol. Survey Bull. 28, Marble Deposits of East Tennessee, by Gordon, Dale, and
Bowles, as recorded in the bibliography at the end of this chapter. This information
was supplemented by that obtained during visits to most of the quarries by the
author.

182

THE iSTONE INDUSTRIES

The belts of the Knoxville district are shown in figure 30, which is
modified from Gordon's index map.^^ The seven belts shown in the
figure lie in approximately parallel positions running southwest and
represent a series of folds resulting from lateral pressure exerted northwest-
southeast. Named in order, from northwest to southeast, they are : Luttrell
belt. Black Oak belt, Concord belt, Knoxville belt, French Broad belt.
Meadow belt, and Bays Mountain belt. The Galbraith belt in Hawkins
County is regarded as a continuation of the Black Oak belt. The
Meadow belt was described later than the others and does not appear in
the sketch. Although some good marble is quarried near the boundaries

Fig. 30. — Map showing marble deposits of eastern Tennessee.

of the formation, by far the best and most productive quarries are those
near the middle of the area.

Luttrell Belt. — The Luttrell belt about 55 miles long extends from
Hawkins County southwestward without interruption to about 8 miles
north of Knoxville. As it fringes the northwestern boundary of the
basin, it contains much earthy and shaly matter. Good marble abounds
in many places; but owing to narrow outcrops and heavy stripping,
conditions do not favor development.

Black Oak and Galbraith Belt. — The Black Oak belt begins at Corryton
and extends southwestward through Fountain City to a point about 5
miles northwest of Knoxville, where it is interrupted by faulting and

" Work cited, p. 27.

MARBLE 183

erosion. It reappears 6 miles farther on and continues into Monroe
County. Near Corryton the outcrop is one half to three fourths mile
wide, but throughout the remainder of its course rarely exceeds one
fourth mile. Many impure limestone and shale beds appear with the
marble.

A northeastern extension known as the Galbraith belt occurs in
central Hawkins County and in near-by Virginia. Folding at this point
has been so great that the beds are overturned, bringing the Knox
dolomite above the marble, which occurs in massive layers and is pre-
dominantly dark red or chocolate. Splashes of white in places represent
crystallized remains of bryozoans, corals, and other organisms.

Numerous quarries have been opened in this area, and some are the
oldest in the State. The Dougherty or National quarry supplied stone
for the United States Capitol. Much of the marble was used for table
and dresser tops, but with the decline of this fashion and a growing
demand for pink and gray, production has ceased in this vicinity.

Concord Belt. — The southwestern extremity of the Concord belt is at
Sweetwater, whence it extends northeast past Loudon, Lenoir City, and
Concord through the northern outskirts of Knoxville and ends near
Strawberry Plains in a closed loop about 4 miles across. In general,
earthy and shaly beds are less prominent than in the belts to the north,
while the marble becomes proportionally thicker, except in a section near
Knoxville where the belt is thin. The Southern Railway follows this belt
closely throughout its entire length, and in several places the Tennessee
River intersects it.

Knoxville Belt. — The KJnoxville belt, where much excellent marble is
quarried, appears several miles southeast of Sweetwater, Monroe County,
and extends northeast through Friendsville, Louisville, and southern
Knoxville to the vicinity of Ruggles Ferry on the Holston River. Near
the two extremities of the belt the rocks dip southeast at an angle of
about 30°, but near Louisville they lie more nearly horizontal. This
accounts for the wide outcrop which appears just beyond the northern
corner of the Friendsville area, as shown on the map. Many quarries
have been opened on the belt from the railway station at Meadow to the
northern extremity. The prevailing marble is a popular shade of pink,
with smaller quantities of chocolate and gray.

French Broad Belt. — The French Broad belt is shaped like a great
U, with its base about 3 miles southeast of Knoxville and its sides extend-
ing northeast 8 or 9 miles. Locally it is sometimes called the " wishbone."
The shape is due to the planing off by erosion of a southwestern pitching
anticlinal fold. The northern arm of this fold is the center of a thriving
quarry industry. The marble formation is about 300 feet thick, and
about half is of commercial grade. Several active quarries are situated
near the junction of the Holston and French Broad Rivers.

184 THE STONE INDUSTRIES

Meadow Belt. — The Meadow belt, which is not shown on the map as a
separate band, is quite close to the Knoxville belt. It has been traced
from near Miser southwestward to a point beyond the railway station at
Meadow, at which place it has been quarried to some extent.

Bays Mountain Belt. — This, the southernmost of the marble belts,
is situated along the north side of Bays Mountain 5 to 7 miles southeast
of Knoxville. It is chiefly in Knox County, though it extends a short
distance into Blount County. The widest outcrop is near Neubert
Springs, where the exposure forms the base of a U-shaped loop which
opens to the southwest as the result of the planing off by erosion of a
northeast-pitching anticlinal fold. As this belt is near the southern
boundary of the marble basin it contains more silty and shaly materials
than the central belts. The beds have a maximum thickness of about
300 feet.

Productive Areas. — The Hawkins County area, which is now unpro-
ductive, has been described briefly in the section devoted to the Galbraith
belt. The five productive areas outlined in rectangles on the sketch
map, figure 30, and designated 1, 2, 3, 4, and 5, are briefly described in
order as follows.

LUTTRELL AREA. — The Only important quarries are at Luttrell and
are situated on the lowest bed of the Luttrell belt. This bed is about 75
feet thick and dips 32° in a direction S.35°E. Mud seams 12 to 20 feet
apart run N.50° to 55°E. A series of seams or cutters spaced at moderate
intervals runs N.60° to 80°W. A light red shading into dark red marble
of good quality is obtained, and waste is burned into lime.

CONCORD AREA. — Several quarries are, or have been, in operation
near Concord on the Black Oak, Concord, and Knoxville belts. A
quarry which was at one time of considerable importance is on a westward
continuation of the Black Oak belt about 3 miles north of Ebenezer.
It was opened on a shallow synclinal fold, and the relatively thin
layer of overburden and nearly level attitude of the beds offered favorable
quarry conditions. The main ledge is a 50-foot bed of light pink marble
with heavy ledges of dark red or "cedar" marble above and below.
Originally only the dark red was quarried, but later both types were
marketed. A prominent series of nearly vertical seams or cutters runs
N.40°W. They are spaced 8 to 20 feet apart throughout most of the
quarry.

The most prominent beds quarried at Concord are 75 to 80 feet thick,
with deep red or chocolate marble in the upper part and light red shading
to pink in the lower. The beds dip 30° to 40°, while irregular mud seams
are nearly fiat or slant at a moderate angle. The quarry is near the
river, and in early years much of the product was shipped by water. A
large part of the waste marble has been burned into lime.

MARBLE 185

For many years several quarries were worked about 43-^ miles south
of Ebenezer, but only one has been in operation recently. It is an
important producer and provides an attractive grade of pink marble
known to the trade as ''Bond Pink."

FRiENDSviLLE AREA. — The productive area on the Knoxville and
Meadow marble belts extends from the station at Meadow to Louisville;
Friendsville is about the middle of the district. In this area about 26
active and abandoned quarries have been noted, but not more than five
or six have produced during recent years.

The most southerly active quarries are about 1^ miles west of
McMullen station, where very sound marble occurs in beds about 120
feet thick, the upper 50 feet being red and the remainder light pink to
gray. The principal development has been during the past few years,
and much high-grade marble is now produced.

About 11^ miles east of Friendsville is a second group of active
quarries. As sound, attractive marble is available in large blocks, this is
the most productive part of the district. Pink and red marbles are most
abundant, although gray is also found. The most southerly of the three
openings uncovers beds about 75 feet thick, and the best grade is found in
the lower 25 feet. The marble, covered with a moderate overburden
of sandy soil, dips under the hill at an angle of about 15°. Many mud
seams appear near the surface, but cutters in the rock are rare. At the
second and third openings to the north the overburden becomes much
heavier, and underground methods employing modern electric-driven
equipment are used. Part of the waste is ground and sold as agricultural
limestone. Two miles west of Louisville a similar pink marble is quarried,
and is marketed under the trade name "Anderson Pink." It is of good
quality and available in large, sound blocks.

KNOXVILLE AREA. — The Knoxville area, occupying the center of
the marble valley, is about 3 miles wide and 6 miles long and extends
northeastward from Knoxville along the valley of the Tennessee River
beyond the junction of its tributary streams, the Holston and French
Broad Rivers. An abundance of high-grade rock is available in this
territory and usually at least a dozen quarries are in active operation.

About 43^-^ miles east of Knoxville the deposit is extensive and has
been worked for many years. A group of quarries provides high-quality
light pink and gray marbles, which are well-suited for structural uses and
for carving. Much of the waste is burned into lime. These quarries
are on the northern limb of the French Broad belt, which extends east-
ward through the loop of the river at the Forks. East of the Forks is an
important group of quarries extending about 2 miles east of the river,
where good-quality pink and gray marble is quarried by several companies.
In places, fissures and solution cavities increase the difficulty of quarrying.
The Knoxville belt to the north provides another important quarry area,

186 THE STONE INDUSTRIES

particularly in the section between the Tennessee and Holston Rivers,
\}/2 to 4 miles northeast of Knoxville. In the western part of this section
the beds are 150 to 200 feet thick, with pink marble in the bottom, gray-
above, and some of the darker reds near the top. The chief output is of
the light gray type, which is very attractive for interior decoration.
The quarries farther east produce high-grade, light pink marbles.

NEUBERT SPRINGS AREA. — Marble has been quarried to some
extent on the Bays Mountain belt near Neubert Springs about 8 miles
directly southeast of Knoxville. The bed dips about 75°, an unusually
high angle in the Tennessee district. This area is close to the southern
fringe of the marble valley, so an excessive amount of impure material is
mixed with the good marble. Although pink and gray marbles of good
quality are available, the proportion of waste is high.

Characteristics of Tennessee Marbles, joint systems. — Two com-
plementary sets of major joints prevail throughout the region, one set
striking N.40°-60°E., and the other N.40°-60°W. Weathering tends
to follow the joints, forming solution cavities which have been filled
with residual reddish clay. When the clay is removed the marble
surface in some districts consists of irregular prongs 5 to 20 feet high and
2 to 10 feet apart at the base. As solution tends to follow all planes of
weakness the prongs usually consist of sound high-grade marble. Opera-
tions on these irregular surfaces are known locally as "boulder quarries."

fossil content. — Tennessee marbles consist mainly of calcareous
remains of two kinds of marine invertebrates — crinoids and bryozoa.
Secondary crystallized calcite encloses the crinoidal fragments and fills
the bryozoan cells, as well as all the interstices. Unlike most marbles
those of the Knoxville district are not highly metamorphosed, and multi-
tudes of fossils show no distortion, recrystallization evidently having
involved only slight deformation.

"crowfoot" structure. — The most characteristic structures of
Tennessee marbles are the stylolites known locally as "crowfoot."
They are irregular or zigzag grayish, black, greenish, or reddish suture
planes. The markings, which occur in bands usually 3^f o to 1 inch wide,
generally parallel the bedding and are from a few inches to several feet
apart. These irregular markings appear prominently on marble steps,
floor tile, and wainscoting in innumerable public buildings throughout the
country. The origin of stylolites is somewhat obscure. It is assumed
that they consisted originally of thin bands of carbonaceous and iron-
bearing shales. Percolating acid waters attacked the beds above and
below the shale, dissolving the marble and leaving very irregular surfaces.
The pressure of overlying strata, or that occasioned by folding, forced
the beds together, and with intermeshing of projections above and
below the shale was pressed into all irregularities. Later faulting and
dislocation made the crenelations even more irregular.

MARBLE 187

TEXTURE. — In general, Tennessee marbles consist of calcite grains in
a groundmass of disintegrated bryozoa. Most of them are fine-grained,
but owing to the presence of larger scattered fossils many are variable
in texture. In all but the coarse, dark marbles of Hawkins County the
crinoidal remains, with the secondary calcite about them, make up
approximately one third of the rock and the bryozoa about two thirds.
Because of the fineness and irregularity of the groundmass the rock is
much stronger than uniformly crystallized marbles.

Physical Properties. — Dale-^ has divided Tennessee marbles into six
groups on the basis of color, as follows: (1) Gray; (2) faintly pinkish gray;
(3) pink ^subdivided into light, medium, and dark); (4) fine dark red; (5)
coarse dark red; and (6) variegated. The gray and pale pink varieties
are used most widely. The marbles are of a high degree of purity, with a
calcium carbonate content of about 99 per cent. Even those of chocolate
color have an iron content of not more than 0.5 per cent. Chemical
purity is attributed to the almost exclusively organic origin of the cal-
careous sediments. Tennessee marble is of low porosity, the pore space
averaging, according to tests by the U. S. Bureau of Standards, about
0.5 per cent; it is much lower in some varieties.

The marble of this State is highly resistant to abrasion and therefore
is well-suited for use as floor tile and stair treads. Notable examples of
use are the concourses of the Grand Central and Pennsylvania Stations
in New York, where for many years Tennessee marble tile has withstood
the wear of intensive pedestrian traffic.

Manufacture and Distribution. — Many large, well-equipped mills
are in operation in and about Knoxville, where marble is manufactured
into a great variety of architectural and ornamental forms particularly
for interior use. Great quantities of marble are also shipped in rough
blocks to mills in the larger cities in all parts of the country.

Vermont.27— In 1929 Vermont produced 1,185,100 cubic feet of
building and monumental marble, valued at $4,763,471, or about 29.8 per
cent of the total value of marble produced in the United States during that
year. Production in 1930 amounted to 1,098,080 cubic feet, valued at
$4,206,456; in 1931, 905,280 cubic feet, valued at $3,187,431; and in 1937,
302,100 cubic feet, valued at $1,539,571.

General Features of Marble Belt. — ^The great marble belt of western
Vermont, which is about 80 miles long, lies chiefly between the Green
Mountains and the parallel Taconic Range to the west, a valley
ranging in width from }i mile to 4 miles. To the south, from Pine Hill
to Danby Hill, the marble lies between the Taconic Range and an

2« Dale, T. Nelson, Work cited, p. 146.

2^ The principal data on Vermont marbles were obtained from U. S. Geol. Survey
Bull. 521, The Commercial Marbles of Western Vermont, by T. Nelson Dale, supple-
mented by visits of the author to nearly all the quarries.

188 THE STONE INDUSTRIES

intermediate range and it also extends north of the Taconic Range,
ending between Middlebury and Bristol. A parallel occurrence of
marble, known as the West Rutland belt, is about 6 miles long and
3^^ mile wide. This lies west of Rutland and occupies a minor longitudinal
valley through which the Castleton River flows.

When in normal position a slaty schist overlies the marble, and a
dolomite lies beneath, but in places these relations are disturbed by
faulting. Records of drill cores and data from sections at the quarries
show that the thickness of the marble ranges from 335 to more than 850
feet. The beds were no doubt originally laid down as horizontal lime-
stone strata in the sea bottom, but in consequence of powerful crustal
contraction which operated mostly west-northwest to east-southeast the
limestones were recrystallized into marbles and at the same time intensely
folded and in places even faulted. The strike of the folds is generally
north and south, although in places it varies somewhat. During subse-
quent ages crests of folds were eroded away, leaving the marble exposed.
At a still later period cross fractures were formed through which a dense,
molten-rock magma was injected, forming trap dikes. These are 2 inches
to 25 feet wide but are not numerous.

Important Geologic Features, complexities caused by folding. —
Rocks of the great marble belt of Vermont have been intensely folded.
Most beds are steeply inchned, the only horizontal ones being sections
in the bottoms of the troughs or tops of the arches. As folds are repeated
a single bed may appear in a succession of outcrops and lateral folding
may complicate greatly the problem of tracing their course. For exam-
ple, an offset of one fourth mile in the position of certain well-defined
marble beds at West Rutland has been attributed to a sharp double
lateral fold in the form of the letter S. It will be seen that if the upper
and lower parts of the letter are continued as horizontal lines, the upper
to the right and the lower to the left, they will represent the same bed
following the same direction but will be offset from each other by the
width of the letter.

effect of pitch of folds. — The axes of folds are rarely horizontal,
but the degree of pitch is usually small — 5 to 20°. The practical effect
of the pitch is to cause variation in the distance of a bed from the surface
as a quarry is advanced along the strike. If the advance is made in the
direction of dip a desirable bed plunges deeper and deeper beneath the
surface, and in time reaches a point beyond which it can not be worked
economically. If a quarry is advanced in the opposite direction the bed
gradually comes closer to the surface until it runs out.

joint systems. — Major joints generally appear in systematic arrange-
ment. The most prominent set strikes N.65°-80°W., with a comple-
mentary set N.10°-20°E. A second system strikes N.75°-80°E., with its
complementary system N.10°-20°W. Diagonal joints occur in places.

MARBLE 189

FAULTING. — "Faulting" is a geological term applied to rock fracturing
with movement along the fractured surface, resulting in dislocation or
change in relative position of beds. The amount of dislocation is known
as the "throw" of the fault. Wherever sharp folding is found, faulting is
likely to occur. In many places in western Vermont the displacement is
only a few feet; in others it may be several hundred. When a major
fault plane is encountered in quarrying, the first step is to ascertain the
direction of throw and extent of displacement. Even a skilled geologist
may have difficulty in interpreting the structure, and core drilling may be
necessary before the continuation of the lost beds is discovered.

EFFECT OF DIKES. — Trap dikes usually occur in regions of close
jointing. Small branching dikes may invade the marble on both sides of
the larger ones. Both close jointing and lateral intrusions discourage
quarrying close to dikes. Most dikes in Vermont follow a course about
N.60°-70°E., and the next most prevalent direction is N.25°-40°E.

EFFECT OF EROSION. — Exposurc of marble beds at the surface is due
to removal of overlying schist by erosion, which at the same time carried
away much marble, leaving truncated folds. Where either an anticlinal
fold (arch) or synclinal fold (trough) has been truncated by erosion
remnants of both limbs of the fold must remain in the earth. If only
one appears in an outcrop it may be possible to locate the other by recon-
structing in theory the original structure and estimating its probable
width at the point of truncation. Such a truncated major fold is in
evidence south of West Rutland, for the beds of both the east and west
limbs have been found. Naturally beds on the east side appear in reverse
order to those on the west. Ability to picture reconstruction of the
marble folds has great practical value in facilitating search for remnants
of beds that may be concealed by glacial debris.

EFFECT OF WEATHERING. — Long ceuturics of Weathering on exposed
surfaces or on rock covered with sand or gravel generally have resulted in
alteration of marble to a depth of 15 or 20 feet, and such material must be
discarded as waste. Exceptionally, marble exposed at the surface is of
good quality, but usually some alteration has taken place unless a cover-
ing of glacial till or water-worked clay has protected it from weathering
effects. In some places the imperviousness of clay has preserved the most
delicate glacial striations, and good marble may be quarried within a few
inches of the surface.

General Succession of Beds. — Throughout many parts of the marble
belt a definite succession of workable beds may be traced. Beginning at
the overlying schist the succession as given by Dale^* is as follows: (1)
Upper graphitic marbles; (2) white graphitic and muscovite marbles
alternating; (3) upper clouded light gray marbles; (4) intermediate
dolomite; (5) lower clouded white marbles; (6) lower graphitic marbles.

28 Dale, T. Nelson, Work cited, p. 96.

190 THE STONE INDUSTRIES

The entire succession is present at few, if any, localities; certain beds are
prominent in one region, while others furnish the chief supply at another
point. At West Rutland the average thickness of all workable beds was
estimated by Dale as 783 feet and at Proctor as 616 feet. This belt
no doubt contains an extensive reserve supply of marble.

Character of Marbles. — Commercial marbles that abound throughout
the valley are of a high degree of purity; many consist of 98 to more than
99 per cent calcium carbonate. Porosity is low, and colors are attractive
for interior or exterior use. They are widely known and are used exten-
sively in all parts of the country.

Individual Quarry Districts. — Marble occurrences in the chief produc-
ing districts are briefly described in the following pages, beginning with
the most southerly quarries and advancing toward the northern end of
the belt.

DORSET MOUNTAIN. — The Imperial quarry is in the southern part of
Rutland County about 1}4 miles southwest of Danby on the northeastern
flank of Dorset Mountain and about 700 feet above the railroad. Both
open-pit and underground methods of quarrying have been employed.
The rock is a coarse-grained, faintly cream calcite marble, which is some-
what translucent. Joints are fairly regular, and large sound blocks are
obtainable. Blocks are conveyed to the railroad by means of cable cars
over an inclined railway three fourths of a mile long. The marble is used
for exterior and interior building and for memorials. The Amphitheater
in Arlington Cemetery near Washington, D. C, was built of stone from
this quarry.

The White Stone Brook quarry a short distance south of the
Imperial quarry is served by the same cable-car railway. The beds,
which total about 100 feet in thickness, dip to the east 5 to 10°. The
stone is coarse-grained and white to cream, with faint yellow to greenish
gray streaks and spots. It takes a good polish and is used for interior
and exterior building.

CLARENDON. — The Clarendon quarry is about 3 miles southeast
of West Rutland. The maximum thickness of the beds here is 327 feet.
The upper beds are graphitic marbles, the middle beds are white, lightly
mottled and banded, while the lowest is a variegated graphitic marble.
Major joints strike N.35°W. and are 3 to 7 feet apart. All the marbles
take a high polish and are well-adapted for construction. The products
are standard Vermont marbles that have been used for many years.

WEST RUTLAND, WEST SIDE. — As prcviously stated, the structure at
West Rutland is a truncated anticline, and the quarries fall into two
groups — those on the western limb and those on the eastern. Six large
quarries have been in operation on the west side; only one is now active,
although others are equipped for production. Marble occurs in a variety
of beds, aggregating nearly 200 feet in thickness. Joints are in regular

MARBLE

191

systems, and their direction and spacing are remarkably uniform, even at
depths of 100 to 150 feet. Some of the quarries are very large. Much
high-grade marble has been removed from drifts which extend along the
beds from the original open-pit workings. Very attractive green, blue,
purplish gray, and cream marbles predominate. The products are
employed chiefly for interior decoration.

WEST RUTLAND, EAST SIDE. — The eastern limb of the anticline is the
most productive region in Vermont. Beginning near the railroad station
at West Rutland an almost continuous line of about 12 quarries extends
for nearly 1 mile to the north. Those farthest to the south, including the

Fig. 31. — Starting a tunnel 400 feet beneath the surface in a West Rutland, Vt., marble
quarry. {Courtesy of Vermont Marble Company.)

Covered, New Opening, and Upper Gilson, are in an upper eastern series
of beds, and those to the north are in an adjoining western and lower
series. The quarries are all narrow openings along the strike, and they
follow the dip of the beds, which usually ranges from 35° to 45°E.,
though in places it curves at steeper or flatter angles. The Covered
quarry is the largest in Vermont; it is nearly 400 feet deep and extends
about one fourth mile underground to the south. In places the roof of
the underground workings is more than 100 feet high and is supported
by large square pillars of the original marble beds. An early stage in
projecting a new tunnel is shown in figure 31. At the Main quarries
long drifts have been projected in the direction of the strike until they
meet, which permits the use of electric mine railroads for haulage. In
the Main and in the West Blue quarries Nos. 1, 2, 3, and 4 many distinc-
tive beds are encountered, and high-grade white, bluish, greenish, and

192 THE STONE INDUSTRIES

pink architectural marbles are produced. Thousands of quarry blocks
are kept at West Rutland in a storage yard served by a 50-ton-capacity
gantry crane. Lime is manufactured as a by-product.

PROCTOR. — The beds in this locality dip about 60°E. The quarries
follow the dip downward and extend along the strike. About five large
openings have been made, but recent activity has been confined to the
Sutherland Falls quarry. Typical Proctor marble is bluish white and
translucent. Very extensive marble-finishing shops are operated at
Proctor, and slabs are brought in from various mills up and down the
valley.

PITTSFORD. — During recent years the Pittsford district has attained
increasing importance. The Pittsford Italian quarry, formerly known as
the Turner, is about three fourths mile southwest of the station at Florence
in Pittsford township and intersects the same beds as the Proctor quarries.
The most typical product is a bluish white calcite marble, mottled with
gray. Beds strike N.25°-30°W. and dip 75°E.N.E. Tunnels are
extended along the strike.

The Florentine quarry, which is about 1}^ miles west of the station at
Florence, intersects the upper graphitic beds immediately underlying the
Taconic Range schists. The beds strike N.25°W. and dip 60° to 70°W.
Structurally the beds belong to the east limb of a syncline. The charac-
teristic product is a dark bluish gray graphitic calcite marble, finely
banded with gray and uniformly fine-grained.

The Hollister quarry 1^^ miles northwest of Florence station is a very
old opening, which has been extended to a series of seven quarries known
as Pittsford Valley Nos. 1 to 7. Nos. 2 and 7 are on the well-known
Brandon Italian beds, which have been quarried for many years near
Brandon farther north. These quarries are very deep, and many lofty
chambers and drifts have been formed by removing all the marble except
that left as massive pillars for roof support. The beds strike N.5°W.
and are almost vertical, dipping 80° to nearly 90°E. The typical rock is a
light bluish gray marble, with irregular mottling due to the recurrence
of fine, gray, plicated beds. It takes a high polish, which emphasizes
the mottled effect. Generally the marbles are more bluish than those
at Proctor. In 1931 eight quarries in this district were either oper-
ating or equipped to produce. These quarries are noteworthy for the
production of unusually large, sound blocks. Masses weighing 55 to 65
tons have been quarried for the manufacture of monolithic columns.
The bowl of Scott fountain, Belle Isle, Detroit, was made from a single
block weighing 65 tons obtained from a Pittsford Valley quarry.

BRANDON. — Marble regarded as identical with that obtained in some
Pittsford Valley quarries occurs in an excavation about one half mile
south of Brandon. It is a mottled, light bluish gray rock suitable for
architectural work. A more recently developed quarry has also operated

MARBLE 193

actively in the Brandon area, producing a standard marble characteristic
of this part of the marble belt.

Other quarries have been worked north of Brandon near Middlebury,
Monkton, and Bristol, but they have not been active recently.

Economic Features of the Marble Belt. — A discussion of the western
Vermont marble belt would not be complete without brief consideration
of certain important economic factors. Available water power has been
exceptionally advantageous in developing the industry, for several large
hydroelectric plants on Otter Creek supply power to practically all the
quarries and mills. The sand resources of the marble valley have also
been utilized to provide an abrasive for sawing and surfacing the marble.

The marble beds are extremely folded, with enlargement or thinning
of certain members, and there are numerous faults. Therefore, many
uncertainties confront workers in opening new quarries and in enlarging
those now in operation. To minimize the risk of unwise development
extensive prospect drilling is constantly conducted. Cores are carefully
examined, recorded, and stored in fireproof buildings for future reference.
The great volume of information thus accumulated is of inestimable value
in interpreting geological structures, estimating reserves, and planning
future activity.

Quarry Districts Outside Western Marble Belt. — Although a large part
of the Vermont production is confined to the western belt previously
considered, there are several important quarry districts outside this area.
Four deserve mention, as each produces marble of a type quite distinct
from those already described.

swANTON. — A marble industry has been developed 1 mile southeast of
Swanton, Franklin County, near Lake Champlain in northern Vermont.
The beds are 150 feet thick. The marbles are described as quartzose
dolomites containing fine-grained magnetite. In certain beds the
magnetite has been oxidized to hematite, which makes the rock charac-
teristically reddish. Some of the beds are of uniform color; others are
mottled red and white. The products are known commercially as
"Champlain marbles," and five distinct types are marketed. On
account of the high silica content they are difficult to saw and finish.
They are highly ornamental and particularly adapted for floor tile and
stair treads, as they resist abrasion remarkably well. A finishing mill
is operated in connection with the quarry. Similar marble is obtained
farther south near St. Albans.

ISLE LA MOTTE. — A marble quarry at the south end of Isle La Motte
in Lake Champlain, Grand Isle County, was one of the earliest to be
worked in America, having been opened for lime burning in 1664 and
reopened in 1788 to furnish building stone. The deposit covers several
acres but is shallow. The rock is a fossiliferous calcite marble that has
been recrystallized, largely by chemical processes, with little compression

194 THE STONE INDUSTRIES

or distortion. Crinoid and gastropod fossil casts show their character-
istic circular structure on polished surfaces. The quarried stone is
dark gray but when polished appears almost black, with occasional white
markings. It is classed commercially with black marbles and is used
chiefly for floor tile, base, and wainscoting.

ROXBURY. — A deposit of serpentine 50 to 60 feet wide is quarried
about 1 mile south of Roxbury in Washington County, 14 miles southwest
of Montpelier. The rock was originally a basic dike, probably consisting
of peri'dotite which has altered to serpentine. Polished surfaces are
almost black but are intersected by a network of veins, some of which
consist of white magnesite and others of a mixture of magnesite and
serpentine, which gives a light green color. Stone from later openings is
a lighter green. The color contrasts are exceptionally attractive. The
product is sold as "Vermont verde antique" and is widely employed for
columns, wainscoting, and various other decoratives uses. Verde antique
is also obtained in a northward extension of the belt at Moretown.

ROCHESTER. — Serpentine marbles occur in various parts of Vermont,
and new developments are to be expected. A more recent operation
than that at Roxbury has been noted at Rochester in the extreme north-
western part of Windsor County, where an attractive verde antique is
quarried and shipped to finishing mills in rough blocks. Verde antique is
quarried also at Proctorsville, southern Windsor County.

Marble Mills. — Large mills for sawing marble blocks into slabs and
other rectangular forms are situated at West Rutland, Center Rutland,
and Florence.

Georgia. — In 1929 Georgia produced 676,190 cubic feet of building
and monumental marble, valued at $3,739,825, or about 23.4 per cent
of the total production of the United States. Separate figures are not
available for 1930. Production in 1931 was 497,370 cubic feet, valued
at $3,323,421; and in 1937, 197,340 cubic feet, valued at $1,030,407.

Pickens County: general description. — The marble industry of
Georgia is confined almost entirely to Pickens County in the north-
central part of the State, where narrow belts occur in folded strata
of Cambrian age. Certain well-defined belts have been described and
mapped by Bayley.^^ The Long Swamp Creek belt is about 3 miles
long, beginning 2 miles northeast of Jasper and terminating about 1%
miles north of the railroad station at Tate. Its width ranges from a
few feet to 125 feet; the depth is unknown. It consists of a fine-
grained, even-grained white rock of sugary texture. According to Bay-
ley's analyses, the marble is very pure, containing 97 to 99 per cent total
carbonates. Two analyses show a considerable content of magnesium.
It is folded so closely that its structure is hard to interpret.

2» Bayley, W. S., Geology of the Tate Quadrangle. Geol. Survey of Georgia
Bull. 43, 1928, pp. 75-102.

MARBLE 195

The Marble Hill belt is a hook-shaped area with its barb extending
lyi miles north of Tate post office and the stem curving around to Marble
Hill 2}^ miles to the northeast. Beyond Marble Hill the rock again
appears in two branches, one extending about 1 mile southwest of the
Amicalola quarry and the other southwest about l^i miles toward
Dawsonville. The main section of the belt, which extends from near
Tate post office to a point beyond Marble Hill post office, is about
7}^ miles long; and many quarry openings have been made in this terri-
tory, which provides the great bulk of Georgia commercial marbles.
In general, the marbles are of the high-calcium type containing 93 to
99 per cent calcium carbonate. They are very strong and of low absorp-

FiG. 32. — Diagram showing how truncation of an anticline may furnish a wide e.xposure of a
narrow bed. a, marble bed; 6, to c, marble exposure.

tion, the porosity, according to United States Bureau of Standards tests,
averaging about 0.5 per cent. Varieties recommended for exterior use
have still lower porosity. They are highly crystalline and of sugary
texture. The colors are mostly white, gray, or bluish with subsidiary
pink.

The Keithsburg belt is more extensive than the Marble Hill belt but
is unproductive. Although situated in Cherokee County, it is related
geologically to the system of belts most highly developed in Pickens
County and therefore demands brief treatment at this time. Beginning
about 2 miles southeast of Nelson it curves southwestward to about
2 miles northwest of Canton. The rock, which is exposed in many
places, is chiefly fine-grained and blue-gray, with a distinct schistosity
due to mica flakes. The marbles are too impure for commercial use.
A fourth small parallel exposure, known as the Sharp Mountain Creek
belt, extends southwestward from about 1 mile north of Ball Ground.

The most productive marble quarries of Georgia are confined to a
relatively small area near Tate and Marble Hill, in Pickens County. The

196 THE STONE INDUSTRIES

valley of Long Swamp Creek IJ^ miles east of the railway station at
Tate is nearly one half mile wide and is underlain with marble 6 to 8 feet
beneath the soil. Evidently the unusual width of the deposit is due to
truncation of an anticlinal fold, because the beds dip in opposite directions
on the east and west sides. As indicated in figure 32, the removal of
the top of such a fold by long erosion might provide a surface exposure
(a to b) three or four times as wide as the actual thickness of the belt.
The Creole and the Cherokee quarries are on the west limb of the fold,
and the Etowah is on the east limb. These quarries are described later.

The remarkable attractiveness and uniformity of the marbles in
Pickens County were recognized by early pioneers. The first systematic
quarrying was done about 1840, and in 1842 a small mill with one gang
saw was operated at Marble Hill. Nearly all the early production was
for tombstones, which were hauled many miles by mules or oxen. With
the advent of railways, markets were greatly expanded, and with an
increasing use for marble in the construction field the industry became
firmly established. The products of these great quarries and mills now
reach every section of the country and are employed for memorials, for
exterior and interior building, for numerous ornamental effects, and for
sculpture. A notable example of the last use is the heroic figure of
Abraham Lincoln carved by Daniel Chester French, and placed in that
great American shrine, the Lincoln Memorial, in Washington, D. C.
Reserve beds of marble which cover several square miles to a depth of at
least 185 feet are practically inexhaustible.

Quarries that are now or have recently been active are described
briefly in the following paragraphs. Geographically they fall in two
groups — those of the Tate district and those of the Marble Hill district.

THE TATE QUARRIES. — Near Tate are two comparatively new quarries
known as Silver Gray No. 1 and Silver Gray No. 2. The silver-
tone grayish crystalline marble from these quarries is sold prin-
cipally for monuments. Large quantities of dark blue and clouded
marbles with a white background are produced at the Creole quarry
also close to Tate. Color contrasts are sharp, and the stone is well-
suited for matched panels and other interior decorative effects. Blocks
of large size free from impurities and seams, are obtainable. The marble
works easily and takes a good polish.

The Light Cherokee quarry, situated close to Silver Gray No. 1, is
very large and deep. It furnishes several shades of light and dark
gray coarsely crystallized translucent marbles, which are suitable for both
interior and exterior use. The coloring matter is less pronounced and
more uniformly distributed than in the Creole quarry. The Mezzotint
quarry in the same group furnishes stone characterized by dark gray
wavy veining on a light gray background. It is much used in interiors
of buildings.

MARBLE 197

Marble from the Etowah quarry, within a few hundred yards of the
Creole, is an outstanding type, for while it is of characteristic coarsely
crystalline structure it is colored various delicate tints of pink (sometimes
banded with white and with darker pinks) which are attributed to
finely divided particles of hematite. It is adapted for both interior and
exterior work and is often used as a trim in contrast with white marble,
as well as for wainscoting and tiling.

THE MARBLE HILL QUARRIES. — The sccoud important group of quarries
is near Marble Hill 3 to 4 miles east and northeast of Tate. Most of
them are in a narrow, high-walled valley, through which flows the east
fork of Longswamp Creek. Many years ago one supplied marble for
stair treads and tiling for the Georgia State Capitol. Geologists claim
that the white marbles of this area have resulted from alteration of
dark marble through contact metamorphism from an intrusive mass of
hornblende. The marble is coarse-grained and translucent. Tremolite
and muscovite appear in places and make polishing difficult. The Spring
and the New York quarries, about 100 yards apart, furnish white and
clouded marbles. Stone from the Rosepia quarry, which is not readily
obtainable in large sizes, is fine-grained and therefore quite unlike the
widely used Georgia types. It is pink, with brownish clouding, and is
adapted primarily for interior use. White marble for building, interior
decoration, and monumental purposes is provided by the Kennesaw
quarry, which has been worked for many years and is very large. The
Amicolola quarry is about 1 mile south of the New York. In this district
joints are widely spaced and therefore blocks of large size are available.
Much of the product is pure white. Tremolite, which occurs in small
irregular blades, is the chief accessory mineral.

NORTHERN PICKENS COUNTY. — During reccut years marble of monu-
mental grade has been produced at Whitestone in northern Pickens
County on the Godfrey property, as described by McCallie.^" The best
marble is coarse-grained and light to dark gray. Crushed and pulverized
products are also sold.

STORAGE AND MANUFACTURE. — Much of the marble from the Tate
and Marble Hill districts is manufactured into finished products in very
extensive and well-equipped mills, most of which are operated by one
large quarrying company, and others by manufacturing firms that have
no quarries. There are marble-finishing mills at Tate, Marble Hill,
Marietta, Canton, Nelson, and Ball Ground. A feature of interest in
the quarry region is the operation of great overhead traveling cranes
that convey marble blocks to storage piles. Acres of ground are covered
with blocks waiting their turn for conveyance to mills. Railways provide
transportation between quarries, storage yards, and mills.

^ McCallie, S. W., Marbles of Georgia. Geol. Survey of Georgia Bull. 1, 1907,
pp. 49-50.

198 THE STONE INDUSTRIES

Marbles Outside Pickens County. — Marble deposits have been noted
in several counties outside the widely known Pickens County district,
but few have attained commercial importance. Recent activity has been
confined to a region about 2 miles southwest of Hollysprings in Cherokee
County, where a quarry is operated for the production of green serpentine
marble (verde antique). The rock occurs in a lenslike deposit about
600 feet long, with a maximum width of about 150 feet. Numerous
veins intersecting the massive serpentine make it highly ornamental.
They are of two kinds. A network of narrow veins, ranging from mere
hair lines to one half inch in width and filled with dark green serpentine,
is the most attractive feature of the rock. Larger and more persistent
veins up to 5 inches in width are filled with dolomite and talc; these
veins are sometimes open and cause much waste. As in most verde
antique deposits quarrymen must contend with much unsoundness, but
by cutting in accordance with joints, masses large enough for orna-
mental columns may be obtained. As waste is great and the rock can
not be cut rapidly, quarrying is expensive, but on account of its highly
ornamental character for baseboards, panels, columns, and pedestals
the marble commands a higher price than white varieties. Two types
are marketed, a rich dark green and a light green, both of which have
attractive patterns.

Missouri. — In 1929, 477,010 cubic feet of block marble was produced
in Missouri; it was valued at $927,530, or about 5.8 per cent of the value
of total production for the United States. In 1930, production fell to
395,960 cubic feet, valued at $839,616; in 1931 to 216,730 cubic feet,
valued at $553,291; and in 1937, to 180,860 cubic feet, valued at $445,114.

Carthage District. — The most important marble-producing center in
Missouri is at Carthage, Jasper County. Geologically the rock belongs
to the Burlington division of the Mississippian or Lower Carboniferous.
It is a formation of wide extent in the State and in many places is quarried
as limestone; in fact, the Carthage stone is sometimes described as lime-
stone rather than marble. Buckley and Buehler,^! in their detailed
description of the district consistently speak of the rock as limestone.
However, during the many years since this report was written the rock
has become well-established as a commercial marble.

At Carthage the marble occurs in heavy, coarsely crystalline beds.
It is white to light gray, with a bluish gray tint, although on a tooled
surface it appears almost white. It is uniform in texture and color and
has been recrystallized with little or no evidence of compression or
distortion. In one respect it resembles Tennessee marble, for it is
characterized by the presence of stylolites or suture joints parallel to the
bedding and 2 to 20 inches apart. However, some of them are less desir-

31 Buckley, E. R., and Buehler, H. A., The Quarrying Industry of Missouri.
Missouri Bur. of Geol. and Mines, vol. 2, 2d ser., 1904, pp. 121-134.

MARBLE 199

able than in Tennessee, as they are inchned to weather more rapidly than
the intervening rock. The highest quality of stone used as monument
stock contains only the very finest of them. So-called "tar seams"
containing bituminous matter cause waste in some quarries. Layers of
flint nodules occur in places. The stone takes a good polish, is very
strong, attractive, and enduring, and is used widely for both structural
and monumental purposes.

Several quarries, mostly north of the city, have been opened, but
during recent years production has been chiefly in the hands of one large
company. Some stone is sawed and finished in the district, but much
of it is shipped in rough blocks.

Phenix District. — The marble at Phenix, Greene County, is of the
same geologic age as that at Carthage and resembles the rock from that
place in many respects. It is coarsely crystalline and bluish gray and
occurs in thick beds. Where free from chert or flint nodules, large,
sound, practically flawless blocks of uniform texture may be quarried.
Fortunately, the chert nodules are confined mostly to certain zones or
layers. Suture joints or stylolites occur, as at Carthage; they are 2 to 14
inches apart and range from fine pencil-like markings to wavelike zones 3
inches in width; the larger ones are undesirable. In some beds the rock is
quite fossiliferous, and the color is a little darker than that of the Carthage
marble. A practically inexhaustible supply is available. A large mill is
operated in connection with the quarry, and both mill and quarry are
well-equipped with modern machinery. Both rough and finished stone
is produced for exterior and interior construction.

South Greerifield District. — The Logan quarry at South Greenfield,
Dade County, w^as in operation in 1929 and following years. According
to report, the stone closely resembles Carthage marble.

Joplin District. — South of Joplin, Newton County, beds of the
Mississippian formation similar to those described above are quarried
for the production of interior and exterior marble. The best bed is 9 feet
thick, coarse-grained and fossiliferous at the bottom and dense and
compact near the top. It is uniform in texture and a pleasing gray.
The suture jomts are very tight and only slightly susceptible to weather-
ing. Both rough and finished stone is marketed.

Ozora District.— Crystsdline limestone that may be classed as marble
occurs in eastern Ste. Genevieve County. Much of it is so intersected by
cutters that large, sound blocks are difficult to obtain, on which account
some operations have not been profitable. The most successful quarry
is at Ozora. The beds worked are in the Kimswick formation, which
lies geologically at a higher level than the Burlington, in which the other
marble quarries of the State are located. A very attractive fossiliferous
golden-vein marble sold in rough blocks for interior work has won a good
reputation. The walls of the elevator lobbies in the Department of

200 THE STONE INDUSTRIES

Commerce Building in Washington, D. C, are good examples of its
decorative value.

Alabama. — Building and monumental marble produced in Alabama
in 1929 was reported as amounting to 52,900 cubic feet, valued at $381,-
781, or about 2.4 per cent of the value of the total production for the
United States. Production was considerably higher in 1928. Produc-
tion in 1930 was 99,790 cubic feet, valued at $481,186; in 1931, 46,390
cubic feet valued at $201,976; and in 1937, 57,050 cubic feet, valued at
$313,663.

General Distribution. — The most important marbles of Alabama pass
through southern Talladega and northern Coosa Counties in a continuous
belt about 35 miles long, with a maximum width of 1^^ miles near
Sylacauga. They range in geologic age from Middle Cambrian to Middle
Ordovician. On the southeast the belt is bordered by the Talladega
slate or phyllite and for most of its length on the northwest by the
Knox dolomite. Prouty^^ mentions several occurrences outside this
belt which have not been worked commercially.

Characteristics of Marbles. — The marble beds are at least 200 feet thick
in their best occurrences and usually dip about 30° southeast toward the
slate. There is evidence of intense compression and folding; in conse-
quence, definite systems of j oints have been developed. A high percentage
of waste is caused by the many irregular, radial, and closely spaced joints.

Alabama marbles are mostly white, and some beds provide pure,
flawless material of statuary grade. They are a little finer-grained than
the Vermont and much finer-grained than most of the Georgia marbles.
Layers of light green talc and schist give ornamental patterns or clouding
to some varieties. Some Alabama marbles are translucent. Porosity is
low, averaging according to United States Bureau of Standards tests
about 0.5 per cent, with a somewhat lower percentage in varieties best
adapted for exterior use. The marble is notably pure, consisting of 98
to more than 99 per cent calcium carbonate. The products are widely
known and are marketed in all parts of the country.

Productive Areas. — The most productive region is at Gantts Quarry
about 2 miles southwest of Sylacauga, Talladega County, where very
large open-pit and underground openings have been made. Diagonal
jointing predominates. About 15 beds have been worked, each 4 to 11
feet thick. Because of differences in color and texture of the beds
several standard types are produced. The quarry is well-equipped with
the most modern machinery. In a completely furnished mill adjacent to
the quarry the marble is manufactured into finished products, chiefly for
use in building.

^2 Prouty, W. F., Preliminary Report on the Crystalline and Other Marbles of
Alabama. Geol. Survey of Alabama Bull. 18, 1916, pp. 41-42.

MARBLE 201

A second large quarry is about three fourths mile northeast. For
the most part, joint planes in this locality run with dip and strike, but
occasional diagonal joints result in considerable waste. Some beds are
clouded, and others are a very attractive cream white. Quarry blocks
are shipped chiefly to New York, for manufacture into finished products.

Another quarry has been opened immediately northeast of that
mentioned above. It is operated on the same beds and produces stone
of the same general quaHty. High-quality marbles have been quarried
at various other points on the belt.

Alabama marbles are used for exterior and interior building and
decoration and for monuments. Some of the waste is sold in large
fragments for use as riprap, and much of it is crushed for terrazzo, furnace
flux, or other uses or ground to a fine powder and sold as whiting
substitute.

New York. — Building and monumental marble produced in New
York in 1929 reached a volume of 51,220 cubic feet, valued at $129,202,
which represents about 0.8 per cent of the total production value for the
United States. Production in 1930 was 68,350 cubic feet, valued at
$161,214; in 1931, 22,770 cubic feet, valued at $56,059; and in 1936
9,890 cubic feet, valued at $57,774. Circumstances are somewhat
pecuhar in New York, in that more marble, in both quantity and value,
is sold rough for riprap, stucco, terrazzo, cast stone, and crushed stone
and as marble flour than as dimension stone. Present producing areas
of block marble are confined to Clinton, St. Lawrence, and Dutchess
Counties.

Clinton County. — The Chazy limestone near Plattsburg and Bluff
Point is crystalline enough to take a good polish. Much of it is quite
fossiliferous and furnishes variegated white, gray, and pink marbles suit-
able for interior use. A black marble deposit has been developed near
Plattsburg.

St. Lawrence County. — A belt of pre-Cambrian marble occurs near
Gouverneur. It is medium-textured, is mottled gray and white or solid
blue-gray and takes a lustrous polish. Much of it contains 6 to 7 per
cent magnesium and in a few places is almost pure dolomite. It is used
for both building and monumental work. The main district is about 1
mile southeast of Gouverneur, where several quarries have been operated
for many years. Much of the waste at dimension-stone quarries and the
entire production of others are used as crushed stone for ballast, road
construction, stucco, and cast stone.

Dutchess County. — The productive quarry area of Dutchess County is
about 2 miles northeast of Wingdale. At least two large openings have
been made, the rock dipping about 40° to the east in the south quarry and
50° to 60° west in the north quarry. They yield a uniform white dolomitic
marble of fine, compact texture that has been in wide demand for archi-

202 THE STONE INDUSTRIES

tectural uses. At Wingdale a large, well-equipped marble-finishing mill
is operated.

Other Quarry Districts. — Marbles have been produced at various
other places in New Yoi*k, among them the black marbles of Glens Falls,
the verde antique of Port Henry, and the white marble of Tuckahoe.
The last marble has been used quite extensively as building stone in
New York City but is now used principally for chemical purposes and the
manufacture of cast stone.

Massachusetts. — The volume of building and monumental marble
produced in Massachusetts in 1929 was 19,720 cubic feet, valued at
197,910, or a little more than 0.5 per cent of the total production value
in the United States. Production in 1936 was 9,110 cubic feet valued at
$41,353.

The true marble areas of the State are confined to Berkshire County,
where dolomitic marbles predominate. They are fine- to medium-grained
and of uniform texture and shade from white to gray. Verde antique is
quarried near Springfield, Hampden County.

Marbles of the Berkshire Hills have been quarried near Ashley Falls,
West Stockbridge, and Lee, but during recent years activity has been
confined to the last locality. Two types are produced at Lee — a clouded
and a pure white. Tremolite crystals are present in places and cause
some difficulty because they are harder than marble and on exposure
tend to weather and leave a pitted surface. The stone polishes well and
gives satisfactory service for interior and exterior construction and for
monuments. A large marble-finishing mill is operated near the quarries.

In several places on and near Russel Mountain about 4 miles from
Westfield, Hampden County, very attractive verde antique has been
quarried. Two types of material occur — a 50-foot dike of serpentine,
which is regarded as an alteration product of basic igneous rock, and a
75-foot bed of dolomitic marble impregnated with serpentine. Massive
rock from the dike is of a rich dark green, variegated by bright green
spots. A small finishing mill has been operated intermittently,

California. — In 1929 California produced 14,260 cubic feet of block
marble valued at $71,259, or less than 0.5 per cent of the total production
value for the country. In 1930, 15,740 cubic feet, valued at $50,640;
in 1931, 15,390 cubic feet, valued at $46,399; and in 1932, 10,910 cubic
feet, valued at $35,905, were reported. California marble is used almost
entirely for interior decoration. Numerous deposits have been noted in
at least 28 counties, but most of them are small or inaccessible, and in
many places the rock is too shattered to permit quarrying large, sound
blocks.

A fine-grained, hard, dolomitic marble is quarried near Lone Pine,
Inyo County. The deposit is notable for its varied colors — yellow,
black, and white, as well as white mottled with yellow, gray, and black.

MARBLE 203

Pink, yellow, and gray varieties occur at Columbia, Tuolumne County,
The belt is 150 feet wide, and sound blocks of large size are easily obtain-
able. The numerous limestone deposits of San Bernardino County are
nearly all crystalline enough to be classed as marble, but little recent
production has been noted. A quarry near Volcano, Amador County,
has been operated intermittently for many years for building and monu-
mental marble.

Onyx marbles have been reported from several localities in Cali-
fornia, but production has been small. A veinlike deposit at Suisun,
Solano County, has been designated as onyx or travertine. The onyx
deposits of California have been described by Aubury.^^

Other Marble -producing States. — About 98 per cent of the total
block marble produced in the country is obtained from the eight States
already considered. The remaining 2 per cent originates in numerous
centers that are small factors in present production, but some are interest-
ing and promise much wider development in the future. They are
described briefly by States or Territories in alphabetical order.

Alaska. — Numerous marble deposits in southeastern Alaska have been
described by Burchard.^^ While several companies have operated in
various places production has been confined chiefly to Tokeen on Marble
Island and Calder on Prince of Wales Island. The Calder quarry is on a
bluff about 100 feet above sea level. Metamorphism of the original
limestone probably was caused by an intrusive granite which lies north-
east of the marble. The belt is approximately 3,000 feet wide and at
least 200 feet deep. Three types of marble are quarried — a pure white,
which is the most valuable, a blue-veined white, and a light blue or
mottled variety. The white marble is very pure, as analyses show more
than 99 per cent calcium carbonate. Blocks are conveyed over an
inclined railway to a wharf on deep water at Marble Cove.

At Tokeen a deposit about 2,500 feet wide and not far above water
level includes white, blue-black, and various shades of gray marbles.
They are medium- to fine-grained, take a good polish, and resemble some
Italian varieties. Matched slabs having dark veins on a white back-
ground are much in demand for interior decoration. A high percentage
of waste is occasioned by close and irregular joints.

All Alaska marbles are shipped by freight steamers to finishing mills
on the Pacific coast, the largest being at Tacoma, Wash. To save freight
only perfect blocks are shipped. Finished products are marketed chiefly
throughout the Pacific Coast States.

'' Aubury, Lewis E., The Structural and Industrial Materials of California.
California State Min. Bur. Bull. 38, 1906, pp. 111-114.

3* Burchard, E. F., Marble Resources of Southeastern Alaska. U. S. Geol.
Survey Bull. 682, 1920, p. 118.

204 THE STONE INDUSTRIES

Arizona. — Onyx marbles are the only types produced in Arizona.
The most extensively developed deposit consisting of bedded calcite and
aragonite beautifully colored by iron oxides is at Mayer, Yavapai
County, 15 miles southeast of Prescott. Highly ornamental products
are obtainable from blocks having combined shades of white, green, and
red. The deposit ranges in thickness from a few inches to 25 feet and
covers an area of about 1 square mile. A finishing plant is at Dyersville,
Iowa.

A second deposit is on Camp Creek west of Cave Creek, Maricopa
County, about 52 miles north of Phoenix. It consists of boulders of
calcite and aragonite in soft travertine. After conveyance to a mill at
Phoenix the boulders are cemented together in a solid mass with plaster
of paris and sawed into slabs and blocks for polishing.

Arkansas. — The best-known marbles of Arkansas occur northeast of
Batesville, Independence County. The rock is classed by geologists as
limestone, but it is recrystallized enough to take a good polish and is
therefore classed commercially as marble. It consists of almost pure
calcium carbonate occurring in the Boone chert series of lower Carbonifer-
ous Age. The rock is gray, of oolitic texture, and although more crystal-
line, resembles Bedford limestone. It occurs in beds 3 to 5 feet thick
and being comparatively free from flaws or seams may be obtained in
large, sound blocks suitable for exterior building. It has been used to a
limited extent as monumental stone.

Black marbles of very good quality, occurring in the Fayetteville and
Pitkin formations of Mississippian age, outcrop on the north slope of the
Boston Mountain escarpment. Several quarries have been opened near
Marshall and at other points west of Batesville, and the product is
marketed as "Arkansas Black."

In 1929 a deposit in the Kims wick and Ferndale formations of Ordo-
vician age was developed near Guion, Izard County, about 20 miles north-
west of Batesville. The marble is coarsely crystallized and of a prevailing
light gray; it occurs in approximately horizontal beds. Fair success has
been attained in quarrying it with a wire saw.

A small amount of marble is produced at times near Cartney, Baxter
County.

Colorado. — Marble has been quarried quite extensively on Yule
Creek near Marble in northern Gunnison County, at a point about
10,000 feet above sea level and about 2,000 feet higher than the Crystal
River Railroad. It occurs in massive beds at least 100 feet thick, with
widely spaced joints which permit very large, sound blocks to be quarried.
Pure white marbles almost of statuary grade are obtainable, as well as
faintly clouded and golden-vein types that afford very attractive archi-
tectural effects. A large, well-equipped mill is operated at Marble.
The industry is handicapped somewhat by difficult, costly transportation.

MARBLE 205

The Lincoln Memorial in Washington, D. C, is built mainly of marble
from this quarry. The superstructure of the Tomb of the Unknown
Soldier at Arlington also is of Colorado marble.

Maryland. — Although marbles occur in many localities in Maryland
they have been actively quarried in only two districts during recent years.
White marbles are quarried at Cockeysville, Baltimore County, and
verde antique at Cardiff, Harford County. Years ago a highly orna-
mental conglomerate known as "Potomac marble" was quarried near
Point of Rocks, Frederick County, but there has been no recent
production.

The Cockeysville deposit about 15 miles north of Baltimore is of
Ordovician age and consists of fine-grained, white, dolomitic marble of
uniform texture. Pyrite crystals are quite common, but they are unu-
sually stable, as evidenced by marble structures containing pyrite being
exposed to the weather for over 100 years with no evidence of staining.
Polished Cockeysville marble is of a dazzling whiteness quite noticeable
in structures in many parts of Baltimore. Many monolithic columns
have been manufactured for large buildings. The cheaper grades of this
marble have been sold extensively for residential door steps, a characteris-
tic feature of many houses in Baltimore. The stone has a good reputation
and has been widely used for many years. A well-equipped finishing
mill is operated in connection with the quarry.

A large serpentine area extends from the Susquehanna River near the
Maryland-Pennsylvania boundary southwestward through Harford
County into Baltimore County. Quarries have been worked in various
places, but present production is confined to one large quarry at Cardiff.
The rock is a very attractive, dark green, veined serpentine — a typical
verde antique. Formerly the chief products were granules, terrazzo,
stucco, and sand ; and while these are still important, the principal output
since 1920 is block marble, which is in demand by architects and
builders. During recent years the operation has become increasingly
extensive. The directions of the quarry walls have been altered in the
lower part of the quarry to conform to the major joints, and waste has
been reduced thereby. On account of a heavy overburden of defective
rock underground drifting methods are pursued. Unsound blocks are
manufactured into floor tile and baseboard in a mill at the quarry, and
large, sound blocks are shipped to New York and other cities.

Michigan. — An attractive verde antique was quarried some years
ago in a small way in Marquette County.

Montana. — Marble for interior building purposes, described as jet-
black with a delicate gold vein, has been quarried near Townsend, Broad-
water County. It is shipped in rough blocks. A vein of onyx
marble 65 feet wide in Gallatin County, about 5 miles north of Manhat-
tan, has been worked in a small way since 1930. A silicified, banded,

206 THE STONE INDUSTRIES

ornamental rock known as "Montana onyx" occurs near Virginia City,
Madison County.

New Jersey. — A light green verde antique of attractive veining has
been quarried about 2 miles from Phillipsburg, Warren County.
Although the chief product is terrazzo, wider use of the stone in block
form is in prospect.

North Carolina. — Commercial marble developments of North Carolina
have been confined almost entirely to Cherokee County. The marble
bed, extending across the county in a belt 1,000 feet to about a half mile
wide, is a northward extension of the beds of Fannin County, Ga. It
strikes northeast and dips about 50° southeast. The largest early opera-
tions were near Murphy and Regal, but recent production has been from
a quarry near Marble. Two types of marble are obtained — a dark bluish
gray, some of which is streaked and mottled with white, and a more or less
uniform white stone. Close, irregular jointing at various intersecting
angles has discouraged quarrying in this region, but the joints are more
regular and more widely spaced near Marble than in other parts of the
belt. A large marble-finishing plant has recently been built.

Pennsylvania. — A deposit of white marble in York County has
been worked to a limited extent for local use. White marble was also
quarried quite extensively in past years at King of Prussia, Montgomery
County. Yellowish green serpentine from Chester County has been
used for facing buildings, chiefly in and about Philadelphia and also in
Washington, D. C. This stone weathers too rapidly for satisfactory
exterior use and therefore has not been quarried for many years.

Puerto Rico. — A large, undeveloped deposit of gray marble with
attractive dendritic markings consisting chiefly of manganese oxide occurs
at the surface in the southern part of Puerto Rico. It takes a good
polish and is available in large blocks.

Texas. — There is a deposit of attractive black marble near Marfa,
Brewster County, which was developed to some extent in 1929.

Utah. — An interior building marble is produced in small quantity at
Thistle, Utah County. On account of its unusual markings one
variety is called "birdseye."

Virginia. — A black marble of good quality is quarried near Harrison-
burg, Rockingham County. During recent years it has been used prin-
cipally for terrazzo, but a mill for producing slabs was erected in 1933.

Washington. — Multicolored marble chips for terrazzo floors are pro-
duced in Stevens County.

QUARRY METHODS AND EQUIPMENT

Prospecting. — Marble is a recrystallized — that is, a metamorphosed —
limestone. Metamorphism that converts limestone into marble is usu-
ally brought about by intense pressure and folding. Thus, the direction

MARBLE 207

and thickness of any bed may change abruptly, either laterally or verti-
cally. On this account, marble beds are more uncertain in position and
extent than flat-lying sandstones or limestones, and careful prospecting
is essential to successful marble quarrying. It is extremely unwise to
proceed with development work or with the extension of openings without
reasonable assurance that an available mass of sound, attractive marble is
sufficiently uniform in quality and abundant in supply for profitable
exploitation.

Most marble beds outcrop in long, narrow bands which may extend
many miles and represent truncated edges of folds in the rock; they may
be curved or straight, depending upon the topography and the nature
of the fold. A geologist may, by careful study of outcrops exposed here
and there, obtain a knowledge of the chief structural features and thus
determine the position, thickness, and attitude of beds with fair accuracy.
Geologic maps of marble belts, if carefully made, have inestimable value
to a prospector, for by consulting them he may determine the position
of marble belts beneath the surface and know something of their extent
and attitude.

Knowledge of exposed beds and their continuation beneath the sur-
face is, however, insufficient. The nature and quality of the rock and
extent of reserves can be determined definitely only by drilling. So much
depends upon color, texture, uniformity, and general appearance that
core drilling is necessary, for only by such means can solid samples be
obtained at depth. As a rule, marble can be worked profitably only on a
large scale, and a considerable outlay to determine whether conditions
are favorable is regarded as a justifiable expense. Therefore, the larger
marble companies do very extensive core drilling. The general prin-
ciples of core drilling have been described in chapter IV, and the subject
is presented at this time merely to emphasize its importance in view of
the uncertain and variable character of most marble deposits.

Economic Conditions. — The success of a marble enterprise depends
upon several important considerations quite distinct from the quality
and extent of a deposit. A wise prospective marble producer gives
careful consideration to market demands, prices, transportation facilities,
competitive conditions, availability of labor, wage scale, and other eco-
nomic questions for which a reasonably satisfactory answer should be
obtained before large expenditures are made. Many enterprises have
failed because these matters have not been fully studied.

Quarry Plan. — The chief factors which influence the plan of quarry
operation are dip of the beds, depth of overburden, and uniformity of the
product in the beds; these factors are intimately related. If desirable
beds are thin and dip at steep angles, shallow quarries are worked along
the outcrop, or underground mining is employed. However, thick beds
dipping at steep angles may be worked in deep open pits, as at Knoxville,

208

THE STONE INDUSTRIES

Tenn. If the strata are flat and the desirable bed is near the surface, a
wide, shallow quarry results.

As regards flat-lying uniform beds of great thickness, a heavy over-
burden tends to promote deep quarrying, whereas a light overburden
will encourage the development of wider, shallower pits. If beds are
vertical or steeply inclined a heavy overburden makes deep quarrying or
tunneling almost obligatory, whereas if only light stripping is necessary
greater lateral development is possible in the direction of the strike.

Fig. 33. — Method of channeling marble in Georgia. {Courteny of Georgia Marble Company.)

Quarry plans may be influenced greatly by the quality of the deposit.
For example, if the marble commands a high price, removal of a heavy
overburden over an extended area may be fully justified, or underground
methods might be employed. For a low-priced marble neither plan
might be economically possible.

Channeling. — After a rock surface is cleared of all loose material by
any of the stripping methods described in chapter IV the next step is to
make primary cuts by means of which blocks are separated from solid
beds. As the integrity of blocks must be preserved explosives are used
sparingly. If the upper level of the rock is inferior through ages of
weathering its removal as waste may be expedited by careful use of
explosives; but where sound and serviceable rock is worked, very little,
if any, explosive is employed.

MARBLE 209

Primary cuts are made almost universally with channeling machines,
the general principles of which have been describe^ in the chapter on
limestone. Both steam and compressed-air machines are used in marble
quarrying. The channeling process is illustrated in figure 33.

Sullivan, Ingersoll-Rand, Wardwell, Tysaman, and several other types
of channeling machines are used, and each has its advocates. A favorite
machine is the double-swivel channeler, which can be used for straight
vertical cuts, for undercutting, or for cutting out corners. A few quarries
in which operations are scattered over a wide area, and in which elec-
tricity is not used, employ machines with portable boilers attached.
The "duplex" channeler consists of two machines on a single truck work-
ing in the same channel.

The electric-air channeler is self-contained, as all the mechanism is
on the channeler truck. The air, compressed by a motor-driven "pul-
sator," is never exhausted into the open but simply driven back and
forth under pressure in a closed circuit. The machine may be used for
vertical, inclined, or horizontal channeling.

The chief factors to be considered in channeling are dip of the beds,
soundness, and rift of the deposit. Where the rock is uniform, with no
open bedding planes and no decided rift, channeling may be conducted
on a level floor, a most desirable condition. However, if the beds are
inclined it may be necessary to quarry each bed separately to maintain
uniformity. The removal of right-angled blocks from successive dipping
beds results in an uneven or saw tooth floor, which necessitates con-
struction of an elevated track for the channeling machine. An improved
method of quarrying on dipping beds is to place the channeling-machine
track on the inclined rock surface in the direction of the dip. A balance
weight overcomes the force of gravity which tends to pull the machine
downhill.

The tendency of joints to occur in parallel systems has been pointed
out. The importance of recognizing such systems and quarrying in
accordance with them can scarcely be overestimated. A practical
quarryman realizes that the prime object in marble quarrying is not to
establish high records in rate of channeling or in gross production per man
per month, irrespective of form or quality of the product, but rather to
produce sound blocks of uniform quality. Cuts are, therefore, usually
made perpendicular to or more rarely parallel to joints, and spaced to
reduce to a minimum the number of joints in blocks. In many deposits
one system is prominent, and cross joints are few. Under such con-
ditions it is wise to channel in one direction only — at right angles to the
chief system. Advantage may thus be taken of joints in making cross
breaks. If joint systems permit, cuts are made at right angles to the
direction of rift to take advantage gf the direction of easy splitting in
making cross breaks by drilling and wedging.

210 THE STONE INDUSTRIES

The rate of channeling varies greatly, depending on the hardness of
the marble and convenience of operation. Where the machine works on
an elevated track the daily average is low because so much time is lost
in moving tracks. Recorded average rates range from 25 to 80 square
feet a day for one machine.

Use of Wire Saws in Marble Quarries. — The construction and
operation of wire saws are described in detail in a later chapter on slate.
This method of cutting rather than channeling is followed in many
European marble quarries but has been used to a very limited extent in
cutting American marbles. Wire saws were employed about 1914, with
favorable results, in a large quarry at Marble, Colo., and WeigeF^ has
described their successful use in an Arkansas quarry during 1929.
Companies in Vermont and Tennessee have tried them, with rather
discouraging consequences. They are, however, used in trimming blocks
in quarry yards as described later. There seems to be no valid reason why
this equipment should not prove as successful in quarries as in yards, or
should be less advantageous in American quarries than in those of Europe.
No doubt problems that now confront American operators will be solved
and wire saws will in time be recognized as standard equipment in
quarrying marble as they are already recognized in the quarrying of slate.

Drilling. — A certain amount of channeling is regarded as necessary in
most marble quarries. However, rock masses are separated by drilling
and wedging wherever possible because they are ordinarily much less
expensive than channeling. Drilling and wedging are almost invariably
used for floor cuts.

The tripod, bar drill or quarry bar, gadder, and hammer drill are the
chief types of drills employed. As the name implies, a tripod is a drill
mounted on three iron legs. Its use is confined almost entirely to vertical
holes, and it must be moved to a new position for each hole. The
quarry bar has been described in the chapter on granite. It is used
chiefly for vertical drilling, but a bar of adjustable height may also be
used for projecting holes in horizontal rows in a bench face. A gadder
is a bar held in vertical or inclined position, to which a drill is attached
for making horizontal holes in the face, either in vertical or inclined
rows. Two gadders are shown at the right in figure 36, page 215. The
hammer drill, which has been described, has replaced to a great extent
heavier types of drills in many marble quarries.

Drilling usually follows the direction of the rift or grain of the marble,
thus taking advantage of the ease of splitting. The spacing of holes
ranges from 4 inches to 2 feet, depending on the rift. Drill holes should
be as small as possible without detracting from wedging efficiency;
most hammer-drill holes are 1}^ to 1^^ inches in diameter at the top.

^^See bibliography at the end of this chapter.

MARBLE 211

If the rock is uniform and sound, lines of drill holes may be spaced
regularly to give uniform, rectangular blocks. If unsound or lacking
in uniformity of color or texture, adjustment of the spacing or
direction of the lines of holes may be necessary to avoid waste and to
grade the product properly. Making alternate holes shallow and
intervening holes the full depth of the break desired is common practice.
The depth of each hole is marked on the surface of the rock to guide
workers in selecting wedges.

Wedging. — Wherever possible blocks should be separated by wedging,
particularly where breaks are made to parallel the rift. To obtain a
straight, uniform fracture proper wedges should be used, and they should
be carefully driven . * ' Plug-and-f eather ' ' wedges, as previously described
are universally employed.

A type of wedge that has proved highly successful is one of which the
feathers are 3 feet long and the plug 3 feet 9 inches; the additional 9
inches is required for driving. The feathers are curved on one surface to
fit the drill hole ; the flat surface is perfectly straight and gives a uniform
taper from one end to the other. The important feature is that, with
the wedge in any position, the total diameter of feathers and wedge is
the same at all points. Consequently, when the plug and feathers are
inserted into the drill hole the inner side of each feather is in contact with
the plug and the outer side with the wall of the drill hole throughout its
entire length. Therefore, when the plug is driven the feathers are forced
apart a uniform distance at every point. As a result the pressure
exerted is distributed uniformly over their full length. Straight, even
fractures are thus obtained with much lighter sledging than by any
other method yet devised. In driving wedges it is important that the
strain on all of them should be equal. A more uniform break will result
by giving the rock sufficient time to fracture gradually, therefore wedging
should never be unduly hastened, especially in marble that has no rift.

A pronounced rift is exceptionally advantageous in wedging, for it
may allow comparatively wide spacing of holes and permit extending
floor breaks to double the width of the ordinary marble block. Thus,
a great saving is accomplished, for channel cuts may be made at intervals
of 10 or 12 rather than 5 or 6 feet, and intermediate breaks may be made
by drilling and wedging, which is a less costly method than channeling.

Usually rift parallels bedding; therefore, if the bedding dips at a
steep angle, the rift may be inclined in like manner. If the rift is inclined
and the quarry floor level, the direction in which drill holes are projected
for floor breaks is exceedingly important. In a Colorado quarry where
the floor is level and rift steeply inclined, channel cuts are made parallel
to the strike of the rock. The influence of rift on the process of wedging
under such conditions is shown in figure 34. When the row of key blocks
has been removed and holes are drilled in the direction shown by arrow a

212

THE STONE INDUSTRIES

in the figure, the break made by wedging tends to leave the plane of the
drill holes and slant upward on the rift, thus removing a corner of the
block, as at x. When holes are drilled in the opposite direction, shown
by the arrow 6, if the channel cut is not continued lower than the plane
of the drill holes, the break will be straight, as it will not run down below
the bottom of the channel cut. It is apparent that, to avoid waste by
broken corners and to reduce expense in drilling, the row of key block,s
should be taken out as near as possible to the left side of the quarry, as
shown in the figure, so that most of the drilling may be done in direction b.
Loosening Key Blocks. — In opening up a new floor the first blocks
to be removed are known as "key blocks." Their removal is difficult
because no face is available from which to work. If a band or mass of

Fig. 34. — Diagram showing influence of rift on bottom breaks.

inferior rock traverses a quarry, key blocks may be located therein and
removed readily by blasting into fragments but if key blocks consist of
good marble they are usually preserved. After channels are cut on four
sides the most difficult step is to make a floor break for the first block. A
common method is to insert a slanting iron plate in the bottom of the
channel cut and place the point of a wedge between it and the key block.
When the wedge is driven the entire strain is exerted at the bottom of the
block. A series of such wedges may be placed close together and sledged
in succession. A horizontal rift greatly assists the process. After the
first block has been removed, horizontal bottom holes may be drilled and
the next block broken free by wedging.

Hoisting Out Key Blocks. — Any one of three methods may be used
for hoisting out the first key block. The first is by use of the Lewis pin,
which is adapted only to strong rock. A hole several inches deep is
drilled at the center of the upper surface, and a bar with an eye in the top
is placed in the hole with a wedge at each side of it. The bar is thicker
at the bottom than at the top, so that when pulled upward it tends to
tighten on the wedges, and the block may be lifted out with a derrick
hoist. A second method, which may also be employed in strong rock is
the use of grab hooks. Small pieces may have to be broken from the
corners of adjoining blocks to make room for the hooks. If beds are weak

MARBLE

213

a third method is employed. Chain loops or cables are thrown over the
block from opposite sides and drawn tight.

Subsequent Floor Breaks. — Removal of a row of key blocks provides
a working face from which floor and vertical breaks may be made for
subsequent removal of blocks. Floor breaks are usually made by drilling
and wedging, though horizontal channel cuts may be made under certain
conditions — for example, in driving tunnel headings. Where quarrying
is conducted on a steeply slanting floor the wedging method would incur
the danger of blocks sliding down upon the men the moment they were
broken loose. To overcome this a single hole is drilled at the center
of the floor line, and a light powder charge is exploded in it. The charge
is so small that it makes the floor break without otherwise shattering
the block.

Roof Line Drill Ho/es-y > / / / ' / / /
Tunnel Channel Cuh_

.Channel Cuh

WTTT/TTTT.

Floor Line
Drill Holes-
' / / A

/// /

y/,

/// // // / / / ' / / / / / ///

' / e ' / / /

////

^ ///

Fig. 35. — Diagram illustrating method of driving a tunnel in marble.

Underground Operations. — To follow steeply inclined beds without
the heavy expense of excessive stripping may demand underground
mining. Extracting marble blocks from drifts and tunnels is not uncom-
mon; very extensive underground operations are conducted, particularly
in Vermont. In underground work the most difficult step is to drive
the preliminary opening at the roof. If the drift cuts across the beds
open joints or seams are rarely available, and the heading must be driven
in the solid rock without any assistance from rock structures. A com-
mon method of advancing a tunnel or drift is shown in figure 35. First
a channel cut about 7 feet deep is made, beginning about 3 feet above the
floor and slanting downward to meet the floor line. A row of horizontal
holes is then drilled at the floor and another at the roof, the heading being

6 or 7 feet high. Horizontal holes are also drilled in vertical rows about

7 feet apart. The lower wedge-shaped mass of rock x in the figure is dis-
lodged by blasting in the drill holes below the channel cut. Light charges
of black blasting powder are used so that the marble beneath is not
shattered. The upper overhanging ledge y is then broken down by dis-
charging blasts in the holes above the channel cut. Broken rock is
removed and the process repeated. If the heading is driven parallel

214 THE STONE INDUSTRIES

with the bedding an open seam may be utiHzed for roof or floor. A bed
of soft schist or talc sometimes serves as a cushion to preserve underlying
rock from the effects of blasting.

If a tunnel is driven in beds of high-grade marble the process may be
modified to preserve the blocks. To provide space for removal of key
blocks channel cuts must be made. Horizontal floor cuts may be made
with a channeling machine, a slow process. Vertical cuts may be made
with a reciprocating drill mounted on a rotating head. While operating
it is rotated back and forth through a vertical arc, and thus it cuts a
channel in much the same way as the circle-cutting drill described in the
chapter on sandstone.

When a preliminary heading of sufficient width and length is obtained
channeling machines or drills may be set up on the floor, and operation
proceeds like that in an open quarry. As underground workings are
enlarged pillars of marble 15 to 20 feet square are left for support at
50- to 80-foot intervals, depending upon the strength and stability of
the roof.

In underground work certain complications are encountered which
do not concern open-pit quarrymen. Artificial lighting and ventilation
must be provided, and lateral haulage to open shafts becomes increasingly
difficult. In some extensive workings in Vermont trackage is provided
for hauling blocks through tunnels to hoist derricks at open quarries.
Cable cars or electric trolleys may be used.

Undercutting. — The tunnel method may be modified by enlarging the
quarry floor by an outward inclination of wall cuts. The process is
simple, requiring no additional equipment and no expensive preliminary
operation. A wide floor space is obtained with a minimum of stripping,
and with moderate extension no supporting pillars are present to obstruct
quarry operations. There are, however, certain disadvantages. In
tunneling, the projection of a preliminary opening is costly and may pro-
duce only waste rock, but when once completed the subsequent channel-
ing and drilling are carried on with almost the same facility as in an
open quarry. In undercutting, however, every wall cut is slanting, and
channeling at an angle is slow and relatively expensive. Moreover
blocks of the outer row are angular, resulting in waste.

In extensive undercutting the danger from overhanging rock may be
averted by leaving wing supports of marble at intervals. Undercutting
is employed successfully in many Georgia and Vermont marble quarries.
It is illustrated at the right in figure 36.

Hoisting. — As a step preparatory to hoisting, blocks usually are turned
down by a gang of men with crowbars. The hoist cable may be attached
by grab hooks, chains, or cable slings. Grab hooks are employed only
when rock is hard and coherent. Two holes for the hooks are made on
opposite sides of a block a few inches from the top. The mistake is some-

MARBLE

215

times made of drilling grab hook holes too deep, for the chief strain then
comes not at the tips of the hooks but on the curved parts that are in
contact with the upper edge of the block. Consequently, a corner of
a block may chip off and allow the whole mass to fall. Holes should be
deep enough to allow a firm grip of the rock, but the chief pressure should
fall on the tip of the hook in the bottom of the hole. Also, the rock
should be carefully balanced, as partial rotation may cause the hooks
to slip. A safer method of attachment is to pass a chain completely

Fig. 36.

-A marble quarry showing simultaneous hoisting, channeling and gadding
operations. {Courtesy of Georgia Marble Company.)

around the block, as shown in figure 36. Another method of attachment
is by means of a pair of cable slings, which are quickly handled and per-
mit easy balancing.

Hoisting usually is done by powerful derricks. Masts and booms may
be of wood or steel. Spliced wooden derricks having mast and boom,
each in four pieces, are used in some regions. They are easy to transport
and set up. Many derricks have a lifting capacity of 15 to 18 tons, but
some are much larger. Derrick guys usually are supported by angle-steel
bars set in concrete. The size of a derrick and choice of its location
are governed by the position and inclination of beds and by the plan of
development. Steam, compressed-air, or electric hoists may be used.
Blocks are hoisted from the quarry and loaded on cars in one operation, if

216 THE STONE INDUSTRIES

possible; if a second step is necessary they are placed in a convenient
position for future loading.

Scabbling. — The term "scabbling," as used by quarrymen, denotes
the trimming of blocks to true rectangular form. Where a mill is close
to a quarry this process may be omitted. If situated at a distance, or
if the marble is to be sold in crude form, blocks are scabbled to avoid
carrying waste material. The most common method is by manual labor
with a scabbling pick. Hammer drills and wedges are used occasionally
to remove the more prominent surface irregularities. In Tennessee a
bar drill, mounted on a triangular plank frame resting on the surface
of the block, is used to advantage. Drill holes are sunk in a row, and
their position is guided by the inner edge of the plank base. By driving
wedges in such drill holes an irregular surface is easily slabbed off. Wire
saws are used successfully at some quarries. A number of blocks may be
lined up and trimmed simultaneously with a single wire. Some operators
regard this as the most economical method.

TRANSPORTATION

In some quarry regions mills are situated so favorably that short
hauls only are required. In several eastern localities blocks are loaded
by quarry derricks directly upon transfer cars. For distant haulage
railroad cars and locomotives, electric trolley lines, and tractors are
utilized. Cable cars may be required on steep grades. Teams and
wagons were frequently used in past years, but the present tendency to
consolidate companies into large units and the necessity for greater speed
have led to more general use of rail transport.

EQUIPMENT AND OPERATION IN MILLS AND SHOPS

Most marble quarries of the United States have plants equipped more
or less completely for sawing, polishing, carving, or otherwise preparing
marble for structural and memorial uses. Also in many large cities mills
are operated by independent companies.

Mill Location and Construction. — Mills operated by quarry com-
panies may be close to quarries or in some near-by town. Water supply,
power, and labor conditions are the chief factors that govern location.
Laborers usually are better satisfied if mills are near towns where schools
and other public institutions are more convenient and better equipped
than in comparatively unsettled regions.

The most modern mills are fireproof, and many that are not have
sprinkler systems. In most northern mills hot-air- or steam-heating
systems are used.

Power. — Water, steam, and electricity are sources of power; the last
is the most widely employed. Some large companies develop their own
electric power, while others purchase it from power lines. One motor

MARBLE

217

may provide power for the entire mill, but it is usually advantageous to
employ smaller units. For transmission from fly-wheel to countershaft
pulley two types of belts are employed, a broad one of leather or fabric
and a rope belt. The latter has the advantages of low first cost and of
easy tightening, the pulley designed for this purpose being applied to a
single turn of the rope. Direct water power is commonly transmitted
by gears.

Traveling.^..
Crane

Shop

Traveling
'■Crane

Sl-ock Pile

Shop

-<bang
Saws

Fig. 37. — Convenient track arrangement for a marble mill.

Arrangement of Mill, Shop, and Yard. — The mill is that part of the
finishing plant where gang sawing is done ; all other finishing is classed as
shop work. Stone is a heavy product, consequently the mill, shop, and
yard usually are arranged to permit minimum handling.

Where both sawing and shop work are conducted the mill and shop are
often placed 30 to 60 feet apart, with an overhead traveling crane between.
A convenient arrangement for a large finishing mill is shown in figure 37.
One traveling crane unloads blocks from cars on their arrival at the mill
and either piles them or loads them on transfer cars. A track passes
down the center with gangs on either side, and a small locomotive

218

THE STONE INDUSTRIES

crane spots transfer cars. Beyond the mill is the shop, and at the end
of it another smaller traveling crane loads finished stock on railroad cars.
Sawing. — A first and very important step in milling is sawing the
marble into slabs or rectangular blocks. The gang saws universally
used are similar in construction and operation to those employed in
sandstone and limestone mills, as described in preceding chapters.
Silica sand is the abrasive used most commonly, though in some mills
steel shot are employed, and greater speed in sawing is attained thereby.

'Xa gl: '11

_ -..a^;* ill

Fig. 38. — Gang saw in operation in a marble mill. (Courtesy of Vermont Marble Company.)

Shot are rarely used on marbles that are porous or contain soft veins, as steel
particles may lodge and cause rusty stains or may interfere with later
finishing processes. Slabs usually are sawed parallel to the grain,
though sometimes distinctive markings are obtained by sawing crosswise.
Great saving of material may be effected by sawing parallel with any
joints that may be present in blocks. However, if cuts must parallel
the grain it may be impossible to saw in accordance with the unsoundness.
As a rule, unsound blocks can be sawed to better advantage into cubic
stock than into thin slabs. The rate of sawing varies greatly, depending
on the hardness of the marble. In stone of moderate hardness, the blades
may sink at a rate of 1 to 2 inches an hour; in extremely hard marbles they
may advance not more than 3 or 4 inches during an entire shift. Gang-
saw operation is illustrated in figure 38.

MARBLE 219

Gang-car and transfer-car systems employed in marble mills are similar
to those used in sandstone mills. Some large mills have more than 40
sawing machines and are equipped with every modern contrivance for
handling materials. Sawed blocks and slabs are removed from cars by
overhead cranes or derricks. Cubic stock may be handled with grab
hooks or smooth-faced iron clamps which automatically close upon a
block when under tension. Thin slabs may be removed in the same way
or by cable slings.

Wire saws are used to a limited extent in place of gang saws. Several
blocks may be lined up and sawed simultaneously. The operation
requires little power or attention and gives satisfactory results in uniform
material if slight variation in the thickness of slabs may be allowed.

Shop or Finishing Plant. — All finishing of marble after sawing is
conducted in the shop. Where shops are operated in conjunction with
mills they are usually so situated that sawed material can be transferred
to them with the greatest facility. The shop may be a continuation of
the mill, or the two buildings may be in parallel positions with a traveling
crane between. Various shop operations are described in following
paragraphs.

Coping and Jointing. — "Coping" and "jointing" are terms appHed
to the subdivision of marble slabs into baseboards, tile, or other finished
products by means of Carborundum wheels or saws. In its strict sense
coping is the process of cutting one slab into two without regard to the
finish of edges. In jointing, however, the edges must be true and
square with the face and without chipped corners. Carborundum wheels
generally are employed for jointing because they usually leave so smooth
a surface that edge rubbing is unnecessary. For this operation the wheel
should project through the slab into a groove in the steel bed.

Rubbing. — Slabs and blocks cut to approximate size are squared and
finished on a "rubbing bed," consisting of a horizontal circular bed of
cast iron revolving at moderate speed. Most beds are driven from above
by countershaft and gears, but some are geared underneath. Marble
slabs or blocks held on the surface of the revolving disk to which sand and
water are supplied are worn down to desired dimensions and smoothness.
Carborundum beds are used to some extent for rubbing small pieces.
Curved and irregular surfaces require hand rubbing with Carborundum
bricks or with small pieces of marble supplied with sand and water.

Gritting and Buffing. — Gritting is a process which gives a smoother
surface than rubbing. Emery powder is sometimes used as abrasive for
this purpose. More frequently abrasive bricks are attached to revolving
buffer heads which travel over the surface. The bricks are of silicon
carbide or aluminum oxide, of varying degrees of fineness, depending upon
the finish desired. Gritting produces what is known to the trade as a
"hone" finish. For hand-gritting curved or irregular surfaces, natural

220

THE STONE INDUSTRIES

hone or pumice is used, though artificial abrasives are displacing them
rapidly.

Buffing, the process which gives the final polish to marble, is accom-
plished by guiding over the wetted surface a buffer head of felt or other
material of soft texture. "Putty powder," consisting of tin oxide or a
mixture of tin oxide and oxalic acid, is used as abrasive. Chromium
oxide — a green powder — is also used. Figure 39 shows a buffer or
"Jenny Lind," as it is called in England. Various abrasive heads are

Fig. 39. — A buffer used for gritting and polishing marble surfaces.

Marble Company.)

{Courtesy of Vermont

shown in the foreground. Irregular surfaces are polished by hand with
putty powder on a felt buffer or with a piece of fine sandstone or hone.

Shop Sawing. — Marble blocks are recut in the shop to various shapes
and dimensions. A perforated circular saw, a diamond circular saw, or a
single blade in a straight-cut gang frame may be employed. A perforated-
steel circular saw employing sand or steel shot as abrasive cuts fairly
well, but in many shops it is now replaced by the more rapidly cutting
diamond saw. Circular diamond saws (see figure 40) are 20 to 72 inches
in diameter. The first cost is high, but with care the cost of maintenance
is not excessive. They occupy little space and saw rapidly. An abun-
dance of water is necessary for successful operation, and care must be
exercised to avoid overcrowding. Two diamond saws adjustable for
width may be arranged to work simultaneously on the same shaft.

MARBLE

221

Planing. — Planers are used for cutting moldings and cornices. Usu-
ally the cutting tool is stationary, except for the lateral or vertical
movements necessary for adjustment. The marble slab is carried on a
traveling bed beneath the tool, which scrapes it to the desired thickness
and to a shape governed by the contour of the tool. A great deal of this
work is now done with Carborundum machines.

Fig. 40.

A diamond saw 6 feet in diameter equipped with 125 diamond teeth sawing a
block of marble. (Courtesy of Vermont Marble Company.)

Machining with Carborundum Wheels. — Silicon carbide used as an
abrading- or grinding agent occupies an important place in all modern
marble shops. Carborundum wheels run at high speed, and an abundant
supply of water is directed upon the cutting edge. For straight slabs or
blocks, cutting wheels of several types are in use. The smaller ones
consist of solid Carborundum, or they may have steel centers. Large
wheels are made of iron or steel and have inserted teeth. Other wheels
have steel centers, with rims of silicon carbide which are thicker than the
steel. They are used until the rim is worn down to the thickness of the

222 THE STONE INDUSTRIES

steel, then they may be rerimmed. Carborundum machines are capable
of varied adaptations and can cut curved work, moldings, cornices, and
balusters with great success. The wheel of the machine is a negative of
the desired pattern. The marble block travels on the machine bed
beneath the wheel, which cuts it to the desired shape ; or it may be placed
on a ball-bearing plate and held against the revolving wheel. In cutting
balusters the marble and the Carborundum wheel are brought into
contact while rotating in opposite directions. The peripheral velocity
of the wheel is approximately 5,000 feet a minute, while the baluster
rotates at about 100 revolutions a minute. In fluting or in making
balusters it is advantageous to rough out marble to the general shape
desired before working it with a wheel. If the wheel must remove
considerable material the process is best divided into two operations. A
6 to 10 grit may be used for the roughing operation, which may remove
stone to a depth of three fourths inch under favorable circumstances.
For the finishing cut a 40-grit wheel usually is employed.

Cutting Columns. — Two principal methods are employed for cutting
marble columns. A drum column-cutter is a circular steel drum which
rotates on a vertical axis. Sand or steel shot may be used as the cutting
agent, or the drum may have diamond teeth. The largest diamond-
toothed drum column-cutter on record was used in cutting columns for
the Lincoln Memorial in Washington, D. C. They are 7 feet 5 inches in
diameter and were prepared in sections, each 58 inches long. The drum,
which had 80 diamond teeth, completed a section in 4 to 5 hours.

Drum column-cutters give satisfaction for short columns or for short
sections, as described above. For large monoliths a lathe must be
employed. The marble generally is roughed out by hand to within one
half inch of the finished diameter before being placed in the lathe. As
the column rotates shaping is accomplished with a cutting tool similar to
that used in ordinary machine lathes for turning metal shafts. Actuated
by worm gear or other device, the tool travels slowly back and forth.
For polishing plain columns a lathe may also be used, though fluted
columns are rubbed or polished by hand.

Cutting and Carving. — All complicated patterns or other irregular
designs must be cut by hand. Much of the straight and simple cornice
and molding work formerly shaped with hand tools is now manufactured
with planers or Carborundum machines. Hand carving may be done
with hand tools and hammers but is accomplished much more
rapidly with pneumatic tools.

Sand blasting is commonly used for lettering headstones. A shield
with an opening the size and shape of the inscription area is placed over a
monument. In early practice steel letters were glued on the surface of
the rock in proper position, and a sand blast directed at high pressure
against this surface for a few moments cut down the entire area except

MARBLE 223

that protected by the steel. A httle hand trimming was necessary to
correct irregularities caused by varying hardness of the stone. A more
modern practice, employing a rubberlike "dope" instead of steel, has
been described in the preceding chapter on granite. Much time is saved
by the sand-blasting method, especially when many monuments of the
same size and shape are manufactured.

Handling Material. — Overhead electric traveling cranes are widely
used for handling heavy material. In many shops small stock is handled
with great facility by means of small hand-operated trucks.

WASTE IN QUARRYING AND MANUFACTURE

Regardless of the high quality of any marble deposit there is always
a certain percentage of loss, owing to processes involved in quarrying,
trimming, and manufacture. Imperfections that are present in most
deposits result in further waste. In fact, the final product may be much
less than half the gross amount quarried. The problem of waste is
therefore vitally important to every producer.

To minimize the heavy burden waste disposal places upon his industry
the marble producer first directs attention toward all types of improved
equipment and modern methods of excavation which tend to keep the
proportion of waste to a minimum; he then seeks all possible outlets for
marketing unavoidable waste. The first phase of the problem is pre-
vention of waste; the second is utilization of waste.

Prevention of Waste. — The chief causes of waste are natural imper-
fections, such as joints, strain breaks, impurities, and lack of uniformity
or attractiveness in color and texture. Systematic prospecting and
development of the best beds in a deposit are important steps toward
reducing waste. Making quarry walls parallel to major rock structures,
such as joint systems, is equally important. When quarrying steeply
inclined beds and maintaining a level floor it may be found desirable to
separate blocks parallel to the bedding, to maintain uniformity in the
quality of material in each block. When angular blocks are thus
produced, much waste results if they are cut into cubic stock, as the
corners must be thrown away; when cut into thin slabs waste may be
much less. Various problems of this nature confront every marble
producer.

The more common impurities in marble are silica, pyrite, and mica.
These minerals tend to occur in definite zones or beds, the more impure of
which may be separated and rejected by making cuts parallel to the
bedding. If bands or streaks of undesirable minerals pass diagonally
through blocks, waste may be excessive.

A condition of strain within a marble mass has in certain places
caused so great a proportion of waste that workings have been abandoned.
Usually the rock is under severe compressive stress in one direction only.

224 THE STONE INDUSTRIES

Quarrying relieves the stress at certain points, and consequent expansion
may cause fracturing. Furthermore, expansion of one mass that is in
rigid connection with the main mass still under compression may cause
irregular or oblique fractures to form between the two masses. To
overcome heavy losses from this cause attempts have been made to afford
relief by uniform expansion of as large a mass as possible at once. To
this end, a line of closely spaced, deep drill holes is projected along each
side of the quarry parallel to the direction of compression, and a similar
line across the quarry at right angles to the first line. The rock slowly
expands, crushing the webs between the drill holes and closing the holes
in the transverse row. Some benefit has resulted from the method,
but the problem of overcoming strain breaks has not yet been satis-
factorily solved.

Utilization of Waste. — Although the proportion of waste may be kept
at a minimum by the adoption of economical quarry methods and use of
efficient machinery, the unavoidable waste may still be large. Many
manufacturers in various lines of industry have found that the fabrication
and sale of byproducts from materials otherwise wasted have placed
their industries on a profitable basis. Extensive waste heaps at many
marble quarries testify to the need of greater development along the line
of utilizing as well as avoiding waste. Marble producers are peculiarly
fortunate, in view of the wide field of usefulness for their waste products.
Many commercial marbles are pure calcium carbonate, the uses for which
are very numerous. Some waste is now consumed for burning into lime,
as crushed stone, as agricultural limestone, and in various other ways.
The many potential uses are covered in detail in a later chapter on
crushed and broken limestone.

MARKETING MARBLE

All high-grade marbles have a nationwide market range. Marketing
is somewhat complex, because there are at least five types of agencies
for this purpose. To the first group belong the so-called wholesalers, who
sell marble to the trade chiefly in blocks or as sawed stock. The second
consists of manufacturers who do not own quarries but buy marble
blocks and finish them. Interior marble usually is both finished and set
by them. A third group comprises dealers or contractors who have
neither quarries nor mills but buy finished marble and sell it to cus-
tomers, set in place. Producers who have quarries but no finishing mills
or shops form the fourth agency. They sell their product in blocks to
wholesalers or manufacturers. The fifth and largest group is composed
of manufacturing producers who have quarries, mills, and shops, and
engage in any and all activities of the trade. The merchandising of
unfinished marble within the trade has no set rule or established general
customs. A wholesaler sometimes sells rough blocks direct to owners

MARBLE

225

of buildings in which the marble is to be used, and the owners have the
material sawed and finished.

Marble in the block and in sawed slabs more than 2 inches thick is
sold by the cubic foot ; slabs 2 inches thick and less are sold by the square
foot. To be "merchantable" blocks usually must be at least 5 or 6 feet
long, 3 or more feet wide, and 2 or more feet thick. In some localities a
standard block is 7 by 5 by 4 feet, but great variations in size may occur.
Measurements should as nearly as possible exclude surface irregularities.
Contracts for finished marble in place are usually on a lump-sum
basis. Much of the marble produced is sold on large contracts closed long
before time of delivery.

Marble is classified as to kinds or varieties, and each kind often
exhibits enough variation to require separation into two or more grades.
Rare, beautiful marbles are high-priced but have a limited market ; those
agreeable in tone, texture, and finish and readily obtainable in large
quantities bring a fair price and have a wide market.

IMPORTS AND EXPORTS

The following table compiled by the United States Bureau of Mines
gives imports of marbles for consumption in this country during recent
years :

Marble, Breccia, and Onyx Imported for Consumption in the United States,

1924-1937, BY Kinds

Year

In blocks

Slabs or paving
tile

All other
manu-
factures

Mosaic
cubes

Total
value

Cubic
feet

Value

Super-
ficial feet

Value

1924

654,706

$1,279,351

309,999

$ 97,935

$205,353

$13,158

$1,595,797

1925

642,226

1,327,439

671,561

210,072

257,382

15,265

1,810,158

1926

864,895

1,789,570

403,458

222,230

438,712

7,028

2,457,540

1927

959,241

2,526,582

925,792

306,696

561,990

9,218

3,404,486

1928

586,069

1,673,363

845,464

310,785

483,071

6,126

2,473,345

1929

678,759

1,615,869

649,899

253,267

566,010

1,908

2,437,054

1930

718,233

1,581,839

591,616

254,179

329,279

12,157

2,177,454

1931

252,457

592,342

442,189

164,346

198,833

8,484

964,005

1932

153 , 828

319,088

232,264

71,832

64,724

455,698

1933

63,482

197,472

155,492

66,825

49,769

203

314,269

1934

19,046

126,320

76,184

27,961

32,222

239

186,742

1935

52,573

228,178

85,092

29,846

40,055

1,697

299,776

1936

60,956

257,634

150,364

58,979

43,879

140

360,632

1937

75,467

297,989

214,588

67,789

69,403

180

435,361

226 THE STONE INDUSTRIES

Exports of marble in block form are very much smaller than imports,
averaging about 65,000 cubic feet a year.

TARIFF

The Tariff Act of 1930 provides a duty of 65 cents a cubic foot on
marble in rough blocks and $1.00 a cubic foot if sawed or dressed and over

2 inches thick. Sawed slabs of various sizes and thicknesses carry duties
of from 8 to 13 cents a superficial foot, with an additional charge of

3 cents if rubbed and 6 cents if polished. Manufactured articles, con-
sisting chiefly or entirely of marble, carry a duty of 50'per cent ad valorem.
The duties are essentially the same as under the Tariff Act of 1922.

PRICES

Marbles vary greatly in quality and therefore in price. The price
range may be $1.50 to $7, or even more, a cubic foot. American marbles
for exterior building purposes average about $2 a cubic foot in rough
blocks. Prices of interior rough blocks at the quarry are quite variable,
ranging from $2 to $7 and averaging about $2.40 a cubic foot. Monu-
mental stock in rough blocks averages about $2 to $3 a cubic foot, though
not much domestic marble is sold in this form. Verde antique in large,
sound blocks of attractive color and capable of a fine polish commands
prices of $6 to $8 a cubic foot at the quarry. Onyx marbles vary greatly
in price, depending on appearance and size of blocks. The price may
range from $5 to $15 a cubic foot.

French and Italian marbles sell in New York at $4.50 to $11.50 a
cubic foot depending on quality. In 1931 second-quality Italian marble
was selling at $4.75 to $5.75 a cubic foot. Belgian black marble has sold
in New York at about $1.75 a cubic foot in rough blocks, though in 1929
and 1930 the price was much higher.

Bibliography

The following bibliography comprises the more important books and periodicals
pertaining to marble and the marble industry:

AuBURY, Lewis E. The Structural and Industrial Materials of California. Cali-
fornia State Min. Bur. Bull. 38, 1906, pp. 95-110.
Bayley, W. S. Geology of the Tate Quadrangle, Georgia. Geol. Survey of Georgia

Bull. 43, 1928, 170 pp.
Bowles, Oliver. The Technology of Marble Quarrying. U. S. Bur. of Mines Bull.

106, 1916, 174 pp.
BuRCHARD, Ernest Francis. Marble Resources of Southeastern Alaska, with a

Section on the Geography and Geology by Theodore Chapin. U. S. Geol.

Survey Bull. 682, 1920, 118 pp.
Granite, Marble, and Other Building Stones of the South. Manufacturers

Record 61, vol. 7, pt. 2, 1912, pp. 59-60.
Butts, Charles. Variegated Marble Southeast of Calera, Shelby County, Ala.

Contributions to Economic Geology, 1910, pt. 1, U. S. Geol. Survey Bull. 470,

1911, pp. 237-239.

MARBLE 227

California State Mining Bureau. Marble. Bull. 38, 1906, pp. 95-114.
Dale, T. Nelson. The Commercial Marbles of Western Vermont. TJ. S. Geol.
Survey Bull. 521, 1912, 170 pp.

The Calcite Marble .and Dolomite of Eastern Vermont. U. S. Geol. Survey

BuU. 589, 1915, 67 pp.

Danekbr, Uerome G. The Romance of Georgia Marble. Thompsen-Ellis Co.,
New "york, 1927, 79 pp.

IDarto^, N. H. Marble of White Pine County, Nev. Contributions to Economic
Geology, 1907, pt. 1, Metals and Nonmetals except Fuels, U. S. Geol. Survey
Bull. 340, 1908, pp. 377-380.

Eckel, Edwin C. Building Stones and Clays; Their Origin, Characters, and Exami-
nation. John Wiley & Sons, Inc., New York, 1912, pp. 166-181.

Gordon, Charles H. The Marbles of Tennessee. State Geol. Survey of Tennessee
Extract (D) from Bull. 2, Preliminary Papers on the Mineral Resources of
Tennessee, 1911, 33 pp.

Gordon, Charles H., Dale, T. Nelson, and Bowles, Oliver. Marbles of East
Tennessee. Pt. 1, Occurrence and Distribution; pt. 2, Constitution and Adap-
tations of the Holston Marbles; pt. 3, Technology of Marble Quarrying. Div.
of Geol. State of Tennessee Bull. 28, 1924, 264 pp. (Prepared in cooperation
with the U. S. Geol. Survey, U. S. Bur. of Mines, and the Div. of Geol. State
of Tennessee.)

Kessler, D. W. a Study of Problems Relating to the Maintenance of Interior
Marble. U. S. Bur. of Standards Tech. Paper 350, 1927, 91 pp.

Physical and Chemical Tests of the Commercial Marbles of the United

States. U. S. Bur. of Standards Tech. Paper 123, 1919, 54 pp.

Permeability of Stone. U. S. Bureau of Standards Technol. Paper 305,

1926, 172 pp.

Lent, Frank A. (compiled by). Trade Names and Descriptions of Marbles, Lime-
stones, Sandstones, Granites, and Other Building Stones Quarried in the United
States, Canada, and Other Countries. Stone Publishing Co., New York, 1925,
41pp.

McCallie, S. W. a Preliminary Report on the Marbles of Georgia. Geol. Survey
of Georgia BuU. 1, 2d ed., 1907, 126 pp.

Merrill, George P. The Onyx Marbles; Their Origin, Composition, and Uses
Both Ancient and Modern. U. S. Nat. Museum Rept. for 1893, 1895, pp.
539-585.

Stones for Building and Decoration. John Wiley & Sons, New York, 1910,

551 pp.

Report on Some Carbonic Acid Tests on the Weathering of Marbles and

Limestones. Proc. U. S. Nat. Museum, vol. 49, 1916, pp. 347-349.

Merrill, George P., and Mathews, Edward B. The Building and Decorative
Stones of Maryland, Containing an Account of Their Properties and Distribution.
Maryland Geol. Survey, vol. 2, pt. 2, 1898, pp. 99-119, 171-197.

Mineral Resources of the United States. Chapters on Stone, containing statistical
and general information, published each year by the U. S. Bur. of Mines, Wash-
ington, D. C. (Prior to 1924 published by the U. S. Geol. Survey, Minerals
Yearbook since 1931.)

Newland, D. H. The Quarry Materials of New York — Granite, Gneiss, Trap, and
Marble. New York State Museum Bull. 181, 1916, pp. 176-208.

Parks, William A. Report on the Building and Ornamental Stones of Canada.
Canada Dept. of Mines, Mines Branch, vol. 1, no. 100, 1912, 376 pp.; vol. 2,
no. 203, 1914, 264 pp. ; vol. 3, no. 279, 1914, 304 pp. ; vol. 4, no. 388, 1916, 333 pp. ;
vol. 5, no. 452, 1917, 236 pp.

228 THE STONE INDUSTRIES

Parks, Bryan, Hansell, J. M., and Bonewits, E. E. Black Marbles of Northern
Arkansas: Arkansas State Geol. Survey Inf. Circ. 3, 1932, 51 pp.

Prouty, William Frederick. Preliminary Report on the Crystalline and Other
Marbles of Alabama. Geol. Survey of Alabama Bull. 18, 1916, 212 pp.

Renwick, W. G. Marble and Marble Working. Crosby, Lockwood & Sons,
London, 1909, 226 pp.

Richardson, Charles H. Building Stones and Clays. Syracuse Univ. Book Store,
Syracuse, 1917, pp. 134-228.

Sewell, John Stephen. Chapter on Marble; Marketing of Metals and Minerals,
edited by Spurr and Wormser. McGraw-Hill Book Company, Inc., New York,
1925, pp. 415-426.

Stone (a monthly magazine devoted to the building and monumental stone industries).
Stone Publishing Co., New York.

Tenney, J. B. The Mineral Industries of Arizona. Univ. of Arizona Bull. 125,
1928, pp. 107-108. (Describes onyx.)

Through the Ages. (A magazine devoted to the uses of marble, its universal adapta-
bility, beauty, permanence, and economy.) Nat. Assoc. Marble Dealers,
Baltimore. (Discontinued in 1932.)

Warnes, a. R. Building Stones; Their Properties, Decay, and Preservation.
Ernest Benn, Ltd., London, 1926, 269 pp.

Watson, John. British and Foreign Marbles and Other Ornamental Stone. Cam-
bridge University Press, 1916, 485 pp.

Weigel, W. M. Application of the Wire Saw in Marble Quarrying. Am. Inst.
Min. and Met. Eng. Tech. Pub. 262, 1930, 7 pp.

CHAPTER X
SLATE

DEFINITION

Slate, like marble, belongs to the metamorphic group of rocks.
According to the standard definition established by the American
Society for Testing Materials, it is "a microgranular crystalline stone
derived from argillaceous sediments by regional metamorphism and
characterized by perfect cleavage entirely independent of original bedding,
which cleavage has been induced by pressure within the earth." In
simpler language, it may be defined as a fine-grained rock derived fronT"**!
clays and shales and possessing a cleavage that permits it to be split '^
readily into thin, smooth sheets. The term includes materials differing
widely in color and varying considerably in chemical and mineralogical
composition.

ORIGIN

Except for certain rare varieties of igneous origin formed from volcanic
ash or igneous dikes, slates have originated from sedimentary deposits
consisting largely of clay. Minerals originally present with the clay in
limited quantities include quartz; mica; feldspar; zircon; compounds of
iron, lime, and magnesia; and carbonaceous matter, together with
silicates other than those named. Through many centuries the clays
carried by rivers were laid down as bedded deposits in deep water, and
in later ages they may have been covered with beds of sand, gravel, or
limestone. The pressure of such superimposed beds gradually consoli-
dated the clays into deposits of shale, a laminated rock consisting essen-
tially of clay but without the splitting properties of slate.

Many shales have been subjected to intense metamorphism and have
thereby been altered into slates. The changes brought about by this
process were both chemical and mechanical. The constituent minerals
were transformed into new minerals, such as mica, quartz, chlorite,
magnetite, graphite, tormaline, and various others, and the first three
usually predominated. The mica and chlorite occur as microscopic
flakes. The intense pressure tended to compress the rock and cause it to
expand at right angles to the direction of pressure. The innumerable
tiny flakes of mica and chlorite, formed as a result of metamorphism,
assumed positions with their flat surfaces lying in the plane of flowage
or elongation. Such parallelism of mineral grains resulted in that

229

230 THE STONE INDUSTRIES

tendency to split with ease in one direction which has been termed
"slaty cleavage." As the rock usually is folded and contorted slaty
cleavage may intersect bedding planes at various angles, a feature which
distinguishes slate from shale, for the latter rock shows no tendency to
split, except in a direction parallel to the bedding.

If the process of metamorphism is so incomplete that much of the
clay remains unaltered the slate is termed "clay slate." When the
process is carried farther and little or no clay remains the rock is called
"mica slate." This type possesses greater strength, is denser and more
resistant to absorption, and therefore more enduring than clay slate.
It constitutes practically the entire supply of commercial slate in the
United States. Continued intensive metamorphism of mica slate pro-
duces more complete recrystallization, forming coarser grains and
developing in the rock a schistosity commonly wavy and irregular. Such
highly metamorphosed rocks are known as "phyllites" or "mica schists."

MINERALOGICAL COMPOSITION

One of the most abundant minerals in mica slate is secondary musco-
vite, or white mica, commonly termed "sericite" — a hydrous silicate of
potash and aluminum. It appears in very minute flakes whose outlines
are recognizable only under a microscope with high magnification.
Small grains of quartz also abound and are distributed regularly among
the mica flakes. Usually considerable amounts of the micalike mineral
chlorite are also present. Chlorites are of various kinds, the more
common being hydrous silicates of aluminum and iron or magnesium.
Clay, or kaolin, usually occurs only in small quantities in mica slates,
though it may be quite abundant in clay slates. Minerals of minor
importance are rutile, andalusite, hematite, pyrite, carbonaceous matter,
graphite, feldspar, zircon, tourmaline, calcite, dolomite, and siderite;
very small quantities of many other minerals are commonly identified.
The general range of mineral composition is shown in the following table.

Mineral Composition of Average Slate

Per cent

Mica (sericite) 38-40

Chlorite 6-18

Quartz 31-45

Hematite 3- 6

Rutile 1- IM

CHEMICAL COMPOSITION

Results of many analyses indicate that clays, shales, and slates
differ little in chemical composition, as the changes that occur during
metamorphism are confined largely to rearrangement of chemical elements
into new minerals and to changes in such physical characteristics as
hardness and cleavage. Chemical composition, while of scientific

SLATE 231

interest, has so little economic significance that detailed chemical analyses
tell little or nothing of the true value of slates. Their commercial
adaptability depends chiefly on mineralogical composition, structure, and
texture. The range in composition of average slate, constituents of less
importance being omitted, is as follows:

Range of Chemical Composition of Slate

Per cent Per cent

Silica 50-67 Soda 0.5-4

Alumina 1 1-23 Magnesia 0 . 5-5

Ferric oxide 0 . 5-7 Lime 0 . 3-5

Ferrous oxide 0.5-9 Water above 110°C 2.5-4

Potash 1.5-5.5

PHYSICAL PROPERTIES

Color. — Slates are of various colors, the most common being light and
dark gray, bluish gray, blue-black, red, green, purple, and mottled.
Yellow, brown, and buff are occasionally found but as these colors usually
have resulted from weathering, the slates are rarely of marketable quality.
The color of a slate is determined by its chemical and mineralogical
composition. Gray and bluish gray are due chiefly to the presence of
carbonaceous material and other colors principally to iron compounds.
Slates containing large proportions of finely divided carbonaceous matter
are black. Permanence of color has considerable economic importance,
for although some slates maintain their original colors for many years,
others change to new shades within a comparatively short time. Such
changes may be due to the presence of small quantities of iron-lime-
magnesia carbonates, which decompose readily with the formation of the
yellow hydrous iron oxide, limonite. Moderate, uniform fading may not
be detrimental to appearance and may even produce a more pleasing
effect. However, in replacing broken slates which are subject to color
changes it may be difficult or impossible to match colors.

Green slates are of two types, the unfading and the fading, or "sea
green." The former maintains a green color indefinitely; the latter when
freshly quarried is greenish gray, which after a few years' exposure
changes to brownish gray or buff. This change is not regarded as
evidence of deterioration; it is, in fact, a weather-aging effect that many
architects prefer. Circular and oval green spots occurring in certain
New York and Vermont slates have long attracted attention. They
are probably the result of chemical changes, such as reduction of iron
oxide caused by decay of organisms.

Strength. — Slate, consisting as it does chiefly of very small overlapping
flakes consolidated under pressure, is a strong rock. Tests are commonly
made of compressive strength; elasticity; and modulus of rupture, or
breaking strength. The last property, which is most significant for a
majority of the uses to which slate is put, is determined by measuring the

232 THE STONE INDUSTRIES

breaking load applied at the middle of a bar of slate supported near the
ends. The modulus of rupture of commercial slates is 7,000 to 12,000
pounds a square inch.

Porosity. — Most mica slates of good commercial quality are practically
impervious to moisture, their porosity ranges from 0.02 to about 0.45
per cent. They are therefore well-adapted for sanitary uses.

Electrical Resistance. — Uniformly clear slate free from spots, veins,
or iron-bearing minerals and low in carbon is highly resistant to electric-
ity. Moisture increases its conductivity; hence after quarrying it
usually is seasoned at least three months before use.

Durability. — High-grade slates, consisting essentially of stable silicate
minerals, which are very resistant to weathering, are among the most
durable building materials. However, to obtain the most enduring types
careful selection must be made. Calcium carbonate apparently is the
least desirable constituent of slates designed to resist long exposure,
especially to sulphur fumes, for sulphur trioxide acting on calcium
carbonate forms calcium sulphate, or gypsum, a mineral which expands
greatly during crystallization with disruptive effects. Medium-grade
slates are serviceable for 25 to 50 years, and the highest grades will far
outlive most structures on which they are placed. Ferguson'^ has
recorded that slate quarried near Delta, Pa., in 1734 was used for roofing
seven buildings in succession. In 1930, the seventh building, a hog pen,
was located near Delta. A sample of the slate has been rescued from
this lowly use and is now on exhibit at the United States Bureau of
Mines, Washington, D. C. After nearly 200 years in service it shows no
evidence of deterioration. Even longer periods of use have been known
in the Old World. A slate-roofed Saxon chapel standing in Bradford-on-
Avon, Wiltshire, England, was built in the eighth century, and though
moss-covered it is still in good condition after 1,200 years of constant
exposure to climatic changes. Slate tombs high in the Alps near Oisans,
France (which, from money and jewels found in them, archeologists have
concluded were constructed about 500 B. C), are still in good condition.

STRUCTURAL FEATURES

Bedding. — The shales from which slates originated were deposited
primarily as clay beds. The beds of shale, at first horizontal, were
tilted by subsequent earth movements, and the intense metamorphism
that converted them into slates folded and contorted them. Differences
in conditions of deposition often resulted in variations in color and
texture of successive strata and such variations make possible tracing
folds and contortions on a quarry wall. Bands representing beds of
darker slate are known among quarrymen as "ribbons." In many

36 Ferguson, E. G. W., Peach Bottom Slate Deposits, Pennsylvania. Min. World,
vol. 33, 1910, p. 183.

SLATE 233

deposits the original bedding has been so obHterated that it is extremely
difficult to trace. Recognition of beds is important, for while the slate
in any one bed tends to be uniform for considerable areas, it may differ
greatly in successive beds. Therefore, for the proper development of a
deposit of desirable slate the original bedding must be followed. Thus,
in the Pen Argyl district of Pennsylvania quarries are situated on the
"Albion vein," the "Diamond vein," the "United States vein," or the
"Pennsylvania vein," each of which is of limited thickness. These
so-called veins, or beds, are vertical or dip at steep angles, and their
direction may change with depth. The folds (inclination) of beds have
direct bearing on the location of quarry openings and on plan of
development.

Slaty Cleavage. — Slaty cleavage is the structure which above all
others differentiates slate from other rocks and gives it economic value.
A true slate can be split into thin sheets with smooth, even surfaces.
Some Pennsylvania slates can be split as thin as one thirty-second of an
inch, but such sheets are too thin for practical use. In the manufacture
of blackboard slates uniform, smooth slabs 4 by 6 feet or larger may be
split readily to a thickness of three-eighths or one-half inch. In some
deposits slaty cleavage is less pronounced than in others and the rock
splits with greater difficulty.

Slaty cleavage may parallel beds, though commonly it intersects them
at angles of 5 to 30° and may even cross them at right angles. Most
slates split with the greatest ease when freshly quarried. Repeated
freezing and thawing destroy the splitting quality.

Grain. — Although they split most readily in the direction of slaty
cleavage, many slates have a second direction of splitting which, is less
pronounced, but has economic significance. In slate literature this
second direction is called the "grain," though quarrymen use the terms
"sculp" or "scallop." It is approximately at right angles to slaty
cleavage, usually nearly parallels the cleavage dip, and may commonly
be recognized by lines or striations on the cleavage surface. It seems
to result from mineral orientation, for many minerals lie so that their
flat faces parallel the direction of the slaty cleavage and their long axes
parallel the grain. In some deposits the grain is distinct, whereas in
others there is practically none.

The relative ease with which slate splits in the direction of grain
compared with the difficulty with which it breaks in any other vertical
plane has distinct practical value in subdividing the larger blocks and
reducing them to convenient sizes. In roofing slate the grain should
always parallel the long sides, so that breakage, which is most likely to
occur in the direction of grain, will parallel the dip of the roof.

Joints. — Joints, seams, or "headers" are more or less regular parallel
systems of cracks, or fractures, in rocks, caused by pressure or movement.

234 THE STONE INDUSTRIES

The origin of joints in rocks has been covered in some detail in the
chapter on granite. They may parallel the strike of beds or the direction
of dip, or may run diagonally. There are also horizontal joints, some-
times termed "bottom" or ''flat joints." In the Pennsylvania deposits
curved, or undulating, joints have been noted. An open seam that
parallels the bedding is termed a "loose ribbon."

Ribbons. — "Ribbons" are dark bands a fraction of an inch to several
inches in width intersecting blocks of slate at various angles. They
represent minor beds of somewhat different composition from the main
body of rock. As they always parallel the bedding they serve as markers
or indicators that assist in tracing folded or otherwise contorted beds.
They are characteristic of the Lehigh and Northampton County, Pa.
slates. The "soft-vein" ribbons in these slates usually are rich in
carbonates and carbon and as a rule, disintegrate more readily than
clear slate. Ribbon slate is therefore used for second- or lower-grade
roofing and as structural slate. In "hard-vein" slate, however, most of
the ribbons resist weathering, and this variety may be employed for high-
grade roofing or other exterior uses.

IMPERFECTIONS

Curved or Irregular Cleavage. — Cleavage in other than a straight,
even plane is undesirable in slate, though a small curvature is permissible
for small roofing slate. Blackboards and structural slate products are
subdivided by splitting, and a crooked split necessitates much labor to
reduce the slab to an even plane. A block of slate having curved cleavage
may produce only three slabs of a given thickness, whereas a straight-
splitting block of the same thickness may produce five or six similar slabs.

Slip or False Cleavage. — Slip cleavage is a tendency to split along
incipient joint planes or seams. It usually runs diagonal to the slaty
cleavage, causing waste.

Veins. — Veins are common in slate quarries. They may follow
bedding or cleavage planes, intersect them at various angles, or be very
irregular. Veins of quartz are termed "flints" by quarrymen. Calcite
or "spar" veins are common, as are also those filled with a mixture of
quartz, calcite, dolomite, and possibly chlorite and biotite.

Impurities. — One of the most undesirable impurities in some slates, is
calcium, usually in carbonate form. Its harmful effects have been
mentioned under "Durability." Iron carbonate is sometimes present,,
and its decomposition not only weakens the state, but the resulting ironi
oxides may cause stains. Iron sulphides may oxidize and form spots
and stains. The stabihty of the iron sulphides has been discussed in
some detail in the chapter on marble. The oxidation of iron-bearing
minerals, especially ferrous carbonate, often causes color changes.
Nodules oi flint or q^uartz encountered ia some slates greatly increase the.

SLATE 235

difficulty of working. Carbon usually is regarded as an agent of dis-
integration and is particularly undesirable in electrical slate, as it acts as a
conductor and promotes leakage of current.

USES

Roofing. — In early years roofing was, with minor exceptions, the only
use for slate, and it is still a very important one. Slate is durable, attrac-
tive, noninflammable, and adaptable to the most artistic architectural
effects. There are two grades of roofing slates — standard and the so-
called architectural. Material for standard slates should have straight,
uniform, smooth cleavage, and the color should be permanent, or if it is
subject to change, uniform color aging without deterioration is usually
demanded. In the United States standard slates are sold by the "square "
— enough slate to cover 100 square feet of sloping-roof surface with a
3-inch head lap. In France and England the unit is a "mille," consisting
of 1,200 slates of any given size and 60 additional to cover loss by break-
age. Standard slates range in size from 6 by 10 to 4 by 24 inches, and in
thickness from three-sixteenths to one-fourth inch. The number of
slates required for a square ranges from 85 to 686, according to size.
The weight of a square of average standard roofing slate is about 650
pounds.

Architectural grades have attained prominence during the past 10
years. They meet the demand of modern architecture for rough, rugged
building materials rather than for the smooth, mathematically exact types
formerly popular. Architectural slates may be 1 to 2}4 inches thick
and 2 to 4 feet long. Surfaces may be rough and uneven and colors
variable. For large structures the heavier slates are placed near the
eaves with the smaller and thinner ones toward the ridge. Slates thus
graduated in size and of a variety of blending colors produce very beautiful
architectural effects. Slate slabs set in mastic are also used extensively
for flat roofs, roof promenades, and terraces.

Mill Stock. — While roofing was originally the dominant branch of the
slate industry many other uses have developed. Slate worked up into
slabs of various sizes and shapes is classed as "mill stock." The different
products are described in following paragraphs.

Blackboards and School Slates. — Slate suitable for blackboards and
feuUetim beards must be soft, and also of uniform color and texture.
Sueh material is obtained chiefly from what is known as the "soft-vein"
region of Lehigh and Northampton Counties, Pa. The soft vein is the
northern slate belt, which includes the region in and about Bangor,
East Bangor, Pen Argyl, Danielsville, Slatington, and Slatedale. This
comparatively small area, about 30 miles long, provides most of the
world's production of blackboard slate. Because of their smoothness,

236 THE STONE INDUSTRIES

uniformity, permanence, and attractiveness, slate blackboards are
superior to all other types now in use.

School slates were once commonly used in America, but demand for
them has greatly declined. Foreign demand is considerable, and most of
those now manufactured are exported. As school slates are small their
manufacture permits utilization of the smaller pieces of slate, many of
which otherwise would be wasted. Slate for this purpose is similar to
that used for blackboards, and deposits are confined largely to the same
area.

Structural Slate. — Although roofing slate ordinarily is regarded as
structural material, a distinction is made in the slate industry, the term
"structural slate" being employed for products used chiefly for interior
structural and sanitary purposes. The chief products are mantels,
floor tiles, steps, risers, flagging, skirting or baseboard, window sills,
lavatory slabs, billiard and other table tops, wainscoting, hearths, well
caps, vats, sinks, laundry tubs, grave vaults, sanitary ware, refrigerator
shelves, flour bins, and dough troughs. Soft, even-grained slate, prefer-
ably not highly fissile, is required for such purposes.

Floors and Walks. — Slate is being used in increasing quantities for
ornamental flagging in sidewalks, porches, and sun parlors. Some is
honed and fitted for close joints, but much is used with split or "quarry
cleft" surface and in irregular outline, which permits utilization of much
slate that heretofore has been discarded as waste.

Electrical Slate. — Certain types of slate have very high dielectric
strength and on this account are suitable for electric panels and switch-
boards. Their superior qualities are strength, rigidity, toughness, and
easy workability. Also, they can be matched easily when switchboards
are enlarged. Electrical slate should be low in magnetite, carbon, and
other low-resistance minerals and capable of being cut and drilled
easily without scaling.

Granules and Flour. — Slate crushed to granular form is employed
widely in the manufacture of slate-surfaced composition roofing. Red,
green, blue-black, and gray granules are manufactured from slates having
these natural colors. Granules are also artificially colored to provide
materials for the highly colored roofs demanded by many architects
and home builders. Ground slate is used for surfacing tennis courts
and other playgrounds. Pulverized slate, known as "slate flour," is
used as a filler in paints, road asphalt-surface mixtures, roofing mastic,
and various other products.

HISTORY OF INDUSTRY

European History. — One of the earliest references regarding the use
of slate concerns a slate-roofed chapel at Bradford-on-Avon, England,
built in the eighth century. In the twelfth century thick, rough Welsh

SLATE 237

slates were used. However, it was not until the latter part of the
eighteenth century that the slate industry attained importance, and even
then methods were crude and wasteful. After 1850, with the develop-
ment of foreign trade and extension of railways the Welsh slate industry
grew rapidly. In France the industry made rapid progress about the
same period.

History in America. — The oldest slate quarry on record in America
was opened near Delta, Pa., in 1734. The first quarry in Virginia was
opened about 1787 to provide slate for the roof of the State Capitol,
and in Georgia the first production was in 1850. From these early
beginnings slate quarrying spread to eastern Pennsylvania, New York,
Vermont, and Maine, and between 1870 and 1880 it became a well-
established industry. Welsh slate workers were the originators of the
industry in several districts.

Although production has assumed fair magnitude it has not increased
proportionally with building construction. This is singular in view of
the adaptability and permanence of slate and the satisfactory service
afforded in its many applications.

Reasons for Slow Growth. — As may be noted from the table on the
following page, which shows production over a period of years, the
industry grew rapidly during 1923, and maintained its increased volume
from 1924 to 1926. In the three following years, which were generally
prosperous, there was decided recession. Lack of sustained activity is
due to various causes. It is to be attributed chiefly to the keen competi-
tion that slate must meet in every line of production — a condition
covered more completely in the section on marketing. Other reasons for
slow growth are excessive waste and high cost of quarrying and manu-
facture. These difficulties are being overcome measurably, as will be
shown later.

GENERAL DISTRIBUTION

The active slate-producing districts of the United States are the
Monson district, Me.; the New York- Vermont district, including Wash-
ington County, N. Y., and Rutland County, Vt. ; the Lehigh district,
including Lehigh and Northampton Counties, Pa., and Sussex County,
N. J.; the Peach Bottom district, including Lancaster and York
Counties, Pa., and Harford County, Md.; and the Buckingham
County (Arvonia) and Albemarle County districts of Virginia. The
geographic locations of these areas are shown in figure 41. These
districts produce roofing slate, and some of them also produce mill
stock, roofing granules, and slate flour. Roofing granules, flour, and
some other products have also been manufactured during recent years in
California, Georgia, Tennessee, and Utah.

238

THE STONE INDUSTRIES

PRODUCTION

The following table prepared by the United States Bureau of Mines
shows sales of slate, by uses, from 1926 to 1937. The total quantity and
value given for each use are the totals of the reports of quarrymen (not

Fig. 41. — Map showing principal slate-producing areas in the United States. (Prepared

by H. Herbert Hughes.)

selling agents), and the value is that f.o.b. quarry or nearest point of
shipment.

Slate (Other Than Granules and Flour) Sold by Producers in the United
States, 1926-1937, by Uses

Roofin

g slate

Mill stock

Total

Other uses*
(value;

Year

Squares

Square
feet

Short tons

(100 square
feet)

Value

(approxi-
mate)

Value

1926

465,900

85,079,087

10,278,130

$4,191,185

$ 73,127

219,950

$9,343,399

1927

468,560

4,949,940

9,287,680

3,519,386

135,448

232,280

8,604,774

1928

483 , 280

5,411,332

9,220,170

3,408,304

184,184

232,380

9,003,820

1929

462,120

4,920,766

9,936,480

3,702,145

124 , 524

241,130

8,747,435

1930

340,140

3,359,939

7,917,220

2,755,530

100,732

173,910

6,216,201

1931

277,700

2,364,861

5,794,380

1,754,054

66,904

138,440

4,185,819

1932

144,410

1,072,255

2,840,020

810,443

23,786

74,490

1.906,484

1933

153,170

967,834

2 , 089 , 650

519,078

28,951

73 , 240

1,515,863

1934

137,010

1,033,164

2,113,620

681,959

26,705

66,570

1,641,828

1935

221,630

1,456,041

2,994,470

849,796

35,333

103 , 690

2,341,170

1936

366,130

2,607,402

4,108,450

1,175,668

55,358

165,110

3,838,428

1937

365,800

2,728,109

4,194,160

1,225,645

73 , 554

167,550

4,027,308

* Includes flagstones, walkways, stepping stones, and miscellaneous slate.

SLATE

239

The following table shows distribution of production by States;
The amounts vary from year to year, but the relative production of the
States is fairly constant. The 1929 figures are shown because they are
probably more typical than those for later years.

Slate Sold by Producers in the United States, 1929, by States and Uses

Opera-
tors

Roofing

Mill stock

Other uses
(value)

State

Squares

(100
square

feet)

Value

Square feet

Value

Total value'

1929

1
2

*
*
*

$ 1,315

3,720

14,670

251,880

151,810

35,460

4,580

$ 38,316

204,362

1,967,428

2,214,869

434,628

61,163

702,740

S 613,996

$ 653,627

214,770

634,169
356,934
875,714

754,135

838,531

Pennsylvania

8,011,080
1 , 222 , 660

2,473,838
614,311

4,798,200
3,704,894

Undistributedt

1,035,156

127

462,120

$4,920,766

9,936,480

$3,702,145

$2,622,267

$11,245,178

* Included under "Undistributed."

t Includes output of States entered as (*) above.

INDUSTRY BY STATES"

Because of the unusual conditions prevailing in 1930, 1931, and 1932,
it is deemed advisable to use 1929 figures to indicate the relative standing
of the various States.

Maine. — Sales of slate in Maine in 1929 were valued at $653,627, or
about 5.8 per cent of the total production-value for the United States.
Production in 1930 was valued at $506,322, in 1931 at $257,619; and in
1937 at $388,521. During recent years two large companies have fur-
nished most of the supply, though others have produced at times.

The slate region of Maine lies in about the center of the State in
southern Piscataquis County near Monson, Blanchard, and Brownsville.
Slate occurs in a belt 15 to 20 miles wide, and the commercial beds lie
south of the central granite area. The strike is in general northeast,
and the dip is very steep, ranging from 80° to vertical. The general
structure is obscure.

Monson District. — Production in Maine is confined almost exclusively
to the vicinity of Monson. The commercial beds are of very fine-grained,

" The geology of the various slate districts is based mainly on U. S. Geol. Survey
Bull. 586, Slate in the United States, by T. Nelson Dale.

240 THE STONE INDUSTRIES

dense, uniform, blue-black slate. The slaty cleavage is vertical and
therefore practically parallels the bedding. Originally open-pit methods
were used, but recent production has been principally from underground
workings.

The largest pit, known as the old Pond quarry, is 500 feet long, 100
feet wide, and 250 to 400 feet deep. This opening intersects about
15 beds of slate interbedded w^ith dark gray or black quartzite. The
structure of the slate does not favor open-pit working, chiefly on account
of the vertical cleavage, which weakens the walls. Obviously, water
entering vertical cleavage planes and freezing therein will cause walls to
spall. Furthermore, rock with vertical cleavage is less capable of
sustaining weight than flat-lying masses and will bulge inward and finally
collapse under intense pressure. On this account, operations in recent
years have been confined to certain thick beds of high quality, and
underground methods have been followed. Details of the method are
given in the section dealing with technology.

Workings adjoining the old Pond quarry have been conducted chiefly
on one bed 9 feet thick dipping at about 10° from vertical. The cleavage
is vertical and nearly parallels the strike of the beds, the angle of inter-
section ranging from 5 to 10°. The grain is vertical and perpendicular to
the cleavage. The 9-foot bed and other parallel beds have been quarried
extensively near the Pond quarry and at other points over a distance of
3 miles to the northwest.

Another series of openings is or has been worked about 1 mile south
of Monson village. The chief bed worked is 10 feet thick, stands vertical,
and strikes N.63°E. The cleavage is vertical and nearly parallels the
strike. The grain is vertical and at right angles to the cleavage. For
many years slate was removed from long, narrow, vertical openings, but
the difiiculty of maintaining safe walls at depths of 300 to 350 feet was so
great, especially in view of the inclined open joints occurring frequently
throughout the district, that underground stoping methods were adopted
and have been employed with success.

Various other openings have been made near Monson, and the general
structure is similar in all deposits. Narrow, vertical beds with vertical
cleavage are the most notable characteristics.

Monson slate is especially adaptable for the manufacture of switch-
boards, panels, and other electrical insulators. Not only has it excep-
tionally high dielectric strength, but it is easily cut and drilled, and the
uniform ebonylike surface is attractive. A large percentage of the total
production in this district is electrical slate, though some blackboards
and a limited quantity of sanitary and structural slate are also manu-
factured. Roofing-slate production has always been small, but this
branch of the industry is attaining greater importance.

SLATE 241

Large, well-equipped finishing mills are maintained in the Monson
district. Electrically driven machinery of the most modern type is
employed to saw, plane, rub, polish, and drill slabs of slate with the
utmost accuracy and precision. Monson slate has won an excellent
reputation for both quality and workmanship. The product is trans-
ported by a narrow-gage railway 6 miles long, connecting with the Bangor
and Aroostook Railroad. Winter weather is severe, and difl&culty is
experienced at times from the heavy snowfall.

North Blanchard District. — Many years ago two large quarries were
operated at North Blanchard about 6 miles west of Monson for produc-
tion of electrical, structural, and roofing slate, but no activity has been
reported during recent years. A series of alternating beds of dark gray
slate and quartzite having a total thickness of 50 to 65 feet strikes
N.25° to 37°E., and dips about 80°. The slaty cleavage parallels both
dip and strike and is at right angles to the grain, which is vertical. The
best beds are 4 to 7 feet thick. The quarries are near the railroad.

Brownsville District. — A dark gray slate was quarried many years ago
in southeastern Piscataquis County near Brownsville. Numerous slate
beds over an area more than 160 feet wide are interbedded with quartz-
ites, as in the other districts. The best beds are 6 to 9 feet thick, run
northeast, and dip about 75°. The cleavage approximately parallels
bedding. Roofing slate was the chief product, but no production has
been reported from this district since about 1914.

New York-Vermont. General Features. — An important slate district
extends from Rutland County west-central Vermont into Washington
County, New York. Slate production in Vermont in 1929 was valued at
$3,704,894, or about 33 per cent of the value of total production for the
entire country. Production in 1930 was valued at $2,463,241, in 1931 at
$1,508,518, and in 1937 at $1,431,798. Roofing slate is the chief product,
but material for floors, walks, mill stock, granules, and slate flour is also
produced in large quantities. Production in New York in 1929 was
valued at $838,531, or about 7.5 per cent of the value of total production
for the United States. In 1930 it was valued at $438,619, in 1931 at
$325,476, and in 1937 at $360,064. Granules and slate flour constitute
about three fourths of the production, and roofing slate one fourth.

Geology. — As the area embraced is a continuous geologic unit, it is
discussed as a whole. The geology of the district is complex. The
slates are of two ages — those of Ordovician age including red, bright
green, and black slates and those of Cambrian age including green,
purple, and variegated slates. In some places the Cambrian rocks pro-
trude through the Ordovician, and intense folding and faulting make the
relationships obscure. The slate beds lie in close folds more or less
overturned to the west with eastward-dipping slaty cleavage. Most of

^42 rtiE STONE 7:ndvstr7e&

the Cambrian roofing-slate quarries are close to the boundairy between the
'Cambrian and Ordovician. In general, the slaty cleavage dips eastward
•30 to 50° and either parallels the beds or crosses them at a low angle.
The grain Or sculp is usually vertical bttt variable in direction in different
'quarries. Close jointing in the dip direction occurs in .pilaces. Quaittz
veins, p'yrite crystals, and dikes appear in some areas.
; ■ Varieties and Uses. — The various types of slate with their distribiition
iand uses are described in following paragraphs.

Sea-green > Slate. — The term "sea-green" is applied ^to a varieity of
'slate 'that w-hen first quarried is light gray to slightly greenish gray, but
^hich after a few years' exposure changes to a buff or brownish gray.
'This color-aging is preferred by some architects and builders. As both
the sea-green and unfading green slates are of Cambrian age and evi-
dently belong to the same period of deposition it is difficult to find a reason
for the difference in degree of permanence in color. Generally, the sea-
green slates are found in the region south of a point about 2 miles north
of Poultney, and the unfading green slates north of that point, but
exceptionally the occurrences are reversed. The difference probably is
due to a change in sedimentation, the southern area having more car-
bonate and the northern less carbonate and more chlorite and pyrite.
Some of the sea-green slates are classed as hard, others as soft. They are
used chiefly for roofing and to a small but increasing extent for floors and
walks.

Unfading-green Slate. — The slate termed "unfading green" is greenish
gray, a color it maintains indefinitely. It contains more pyrite and
magnetite than the sea-green and splits less readily. Unfading-green
slate is confined chiefly, though not entirely, to that part of the slate area
which lies north of Poultney. It is used principally for roofing.

Purple and Variegated Slates. — The so-called "purple" slate is dark
purplish brown, the purple color being attributed to a mixture of the red
of hematite with the bluish green of chlorite. The "variegated" is
greenish brown, with irregular purple patches giving a mottled effect,
which is attributed to irregular distribution of hematite. Both types are
interbedded with the sea-green and unfading-green slates but are less
susceptible to color changes than are the sea-green varieties.

Mill-stock Slates. — Certain purple and green slates having poor cleav-
age are used for various milled products, such as floor tile, vats, mantles,
baseboards, sills, steps, and to a small extent billiard-table tops, sanitary
slabs, and blackboards. Some purple slates are well-adapted for elec-
trical uses. Most of the slate used for milling purposes is obtained in
the northern district, near Fair Haven, Vt.

Red Slates. — Red slates associated with bright green varieties of
Ordovician age are found in Washington County, N. Y., near Granville.
The red color is due to abundant hematite. These slates occur in beds

SLATE 243

10 to 25 feet thick, and are used for granules and to a limited extent for
roofing.

Flagging and Building Stone. — Slate for copings, flagging, terraces,
ornamental walkways, and walls made entirely of slate or in combination
with other stones is produced in increasing quantities, particularly in
Washington County, N. Y. Very attractive sidewalks and porch floors
are made by fitting together flagstones of various sizes, shapes, and
colors.

Granules and Slate Flour. — Granules for the manufacture of prepared
roofing are made of both red and green slate at Granville, Middle Gran-
ville, Poultney, and Hampton. Slate is also ground to a fine powder
and sold as a filler for roofing mastic, paint, road asphalt, and various
other products.

General Distribution of Quarries and Mills. — Aside from granules,
flour, and slate for floors, walks, and walls the product of Washington
County, N. Y., is roofing slate. Many slates are of the thick, heavy
types known as architectural grades. Their rough texture and attrac-
tive, variegated colors adapt them for ornamental roofing material. A
few large companies have quarries near Granville and Middle Granville,
and many small quarry operators sell their products to them.

In the southern slate district of Vermont, which extends from Poult-
ney to West Pawlet, the chief product is roofing slate. Numerous
quarries are operated throughout this district and produce slates in a
wide variety of color combinations. Granules are also manufactured,
chiefly from green slates. In the northern district of Vermont, near
Poultney, Fair Haven, and Hydeville both roofing and mill stock are
produced. Several slate-finishing mills are operated, particularly in and
near Fair Haven. Structural, electrical, and roofing slates are important
products of this territory.

It may be observed from the above descriptions that Vermont and
New York produce slates in an attractive variety of colors particularly
well-adapted for roofing high-class residences and larger structures.
The heavy architectural grades are sold widely for ornamental roofs.
With proper color blending and graduation of size they produce effects
unsurpassed in attractiveness by any other roofing material. More
than 20 companies quarry slate in New York and more than 50 companies
in Vermont.

Pennsylvania. Lehigh District. General Features. — The Lehigh dis-
trict comprises Lehigh and Northampton Counties, Pa., and Sussex
County, N.J. The Pennsylvania slates occur in a strip 2 to 4 miles wide
on the south side of Blue Mountain, extending from Delaware Water Gap
on the Delaware River southwest to a point 4 miles west of Lehigh
Gap on the Lehigh River — about 32 miles. Quarries centered chiefly
around Bangor, Pen Argyl, Windgap, and Slatington constitute the most

244 THE STONE INDUSTRIES

productive slate area in the United States. The Sussex County (N. J.)
deposit, extending from Newton and Lafayette to the Delaware River, is
regarded as an eastward continuation of the Pennsylvania beds.

Slate produced in Pennsylvania in 1929 was valued at $4,798,200, or
about 42.7 per cent of the value of total production in the United States.
Production in 1930 was valued at $3,634,258, in 1931 at $2,791,752, and in
1937 at $2,735,744. A small part of the Pennsylvania production was
obtained from the Peach Bottom district, which is considered in a sub-
sequent section of this chapter. Roofing and mill stock are both pro-
duced extensively, and there is a small production of granules and slate
flour.

Geology. — A Cambrian and Ordovician dolomite and limestone plain
3 to 6 miles wide extends north and northeast from Easton, Pa., following
the general direction of the Delaware River as far as Belvidere. The
upper member, the Jacksonburg limestone, provides the well-known
cement rock of the Lehigh Valley. The limestone dips northwest, and
overlying it is the Martinsburg formation, which includes the slate beds.
At the southeast the shales and slates are in contact with the underlying
limestone and at the northwest dip under the Silurian conglomerate and
sandstone of Blue Mountain. The slate belt is 1,600 to 6,000 feet wide,
but only a few hundred feet are of commercial quality.

The slate formation consists of two lithologically different rock types.
The lower section, known as the "hard-vein" belt is made up of hard
closely bedded slates interbedded in places with sandstone. It occurs
farthest south passing through Belfast and Chapman Quarries. Above
it are beds of nearly pure sandstone, and higher still, a second type of
slate, which is soft and thick-bedded, with occasional sandy layers.
The upper section constitutes the "soft-vein" belt, which extends from
East Bangor through Bangor, Pen Argyl, Windgap, Danielsville, and
Slatington to Slatedale. From the structural relations it is evident that
the soft-vein slate everywhere occurs nearest the mountain.

The slate beds consist of a succession of close folds generally over-
turned northward so that their axial planes have a general southerly dip.
Folds are easily recognized by the curve of the ribbon. The slaty
cleavage dips southward at various angles, usually ranging from 5 to 20°,
and therefore intersects the ribbon at a high angle.

Varieties and Uses. Hard-vein Slate. — "Hard-vein" slate, as the
name implies, is relatively hard compared with the overlying beds. It is
used almost exclusively for roofing, walks, and masonry walls, as it is too
hard for milling. The rock is blue-gray, with somewhat darker carbon-
aceous beds. The more siliceous beds have a faintly silvery sheen.
Ribbons, consisting mostly of siliceous minerals highly resistant to
weathering, are numerous and closely spaced. They scarcely deflect
the cleavage, which is remarkably well-developed.

SLATE 245

CHAPMAN QUARRIES DISTRICT. — The most productivG district in the
hard-vein belt is at Chapman Quarries station on the Lehigh & New
England Railway. Quarrying began in this district about 1860.
Numerous openings have been made, but only two or three of the
largest have been quarried actively during recent years. The slate beds
in this area are folded and contorted, synclines and anticlines appearing
on quarry walls. The slaty cleavage, however, is remarkably constant,
generally ranging from 10 to 20° in a southerly direction. The principal
joints, which strike about N.60°E., are nearly vertical and form many
of the smooth faces seen on quarry walls. The grain is vertical and
strikes N.37°-53°W. While variations occur in different quarries the
general structure is much the same throughout the district. For many
years the larger quarries have continuously produced large quantities of
roofing slate. Heavy, rough-textured architectural slates are produced
in increasing quantities, and heavy flagging and grave vaults are made in
limited amounts.

BELFAST-EDELMAN DISTRICT. — Typical hard-vein slate of this area
lies within a radius of 23-^ miles of Edelman on the Delaware, Lackawanna,
& Western Railway. Only two quarries have been active recently, one
at Edelman and one at Belfast. In the Edelman quarry major joints
strike in a general northeasterly direction and are quite regular. Slaty
cleavage dipping about 10°S. cuts across the intensely folded beds. A
vertical grain trends about N.50°W. In the Belfast quarry the cleavage
dips east at angles of 5 to 22°, while the grain trends about N.40°W. and
is vertical. Roofing slate is the main product.

Soft-vein Slate. — The upper soft-vein member of the Martinsburg
formation consists of thick beds of light to dark bluish gray slate alter-
nating with thinner, almost black beds (ribbons). The wider ribbon-free
bands are known as "big beds"; they are particularly prized, as they
provide clear stock for blackboards and other of the higher-priced
products. Ribbons, which consist of thin carbonaceous beds, have an
important bearing on the value of slate, for most of them disintegrate
upon exposure a little more rapidly than the main body. For this reason
ribboned slate is not favored for the most enduring uses, though some of
it will give good service for 50 or more years. Because of their carbon
content ribbons are not good electrical insulators and therefore must be
avoided in the manufacture of switchboards and panels. For certain
exposed uses they detract from appearance, but as they do not affect
strength greatly, ribbon slate is widely used for many structural applica-
tions, such as steps, risers, baseboard, wainscoting, etc. Its easy
workability makes soft-vein slate particularly desirable mill stock.

"Hard rolls" is a name given to the sandy portions of beds which are
usually discarded, partly because they dull tools rapidly and are therefore
worked with difficulty and partly because the cleavage is inclined to be

246 THE STONE INDUSTRIES

curved or irregular. Siliceous knots, which are present in places, affect
the workability of the slate and cause uneven cleavage.

In the eastern or Bangor-Pen Argyl part of this region, the soft-vein
member of the Martinsburg formation may be separated into two parts —
the lower or Bangor beds and the upper or Pen Argyl beds. The former
extend from East Bangor through Bangor and thence southwestward,
passing from }^ to l^z miles south of Pen Argyl. The upper beds pass
through the southern part of the town of Pen Argyl and through West
Pen Argyl and Windgap. It is customary in the Pen Argyl and Bangor
districts to recognize certain subdivisions called "runs," which include the
several beds of slate exposed in a quarry or group of quarries. Generally
accepted names are applied to the more important runs, and the slate in
some instances is well-known to the trade by the name of the run from
which it is obtained. In general, the slate of any particular run is fairly
constant in quality from one quarry to another, although variations occur.

BANGOR DISTRICT. — The lower beds of soft-vein slate are slightly
harder than the upper, and ribbons are somewhat closer together.
Beginning at the top of the Bangor beds, the following runs generally are
recognized: North Bangor No. 3, North Bangor No. 2, North Bangor,
Bangor Union, Old Bangor, and Grand Central. Each is subdivided into
certain characteristic beds on the basis of thickness, ribbon, and color.
Seven or eight companies operate quarries near Bangor and East Bangor,
where more than 30 quarries are or have been active. The main product
is roofing slate which has won a high reputation through many years of
satisfactory service. Some beds are suitable for mill stock, and several
large mills are operated. Certain thin beds intermediate in color between
the carbonaceous black of the ribbons and the light gray of the big beds
are used for school slates.

PEN ARGYL AND WINDGAP DISTRICT. — The Upper soft-vcin slates that
extend southwest from Pen Argyl are grouped into well-recognized runs
in the same manner as those at Bangor. Beginning with the topmost
beds the following runs appear in succession: Pennsylvania, United
States, Diamond, Albion, Acme, and Phoenix. The runs are not in
direct contact with each other but are separated by intervening beds
75 to 280 feet thick, consisting of unworkable slaty rock. Each run is
made up of a series of individual beds; the Albion run, for example,
consists of 12 beds with an aggregate thickness of 184 feet; some are big
beds, some ribboned slate, and others unworkable rock. The Albion
"gray bed" is of exceptionally high quality.

Eight or 10 companies operate quarries in and about Pen Argyl.
The largest and deepest open-pit slate quarries in the country are in this
territory; a maximum depth of 725 feet has been attained, and depths of
400 to 500 feet are not uncommon. Deep quarrying is not entirely a
matter of choice; it is influenced by rock structures. Beds dip at very

SLATE

247

steep angles and in places are almost vertical. As property lines or heavy
overburden in many places restricts extension of quarries along the strike
and as beds are of limited thickness, a great volume of production can be
attained only by following the beds to greater and greater depths.

Rock structures are favorable for quarrying. Slaty cleavage gener-
ally dips south at a low angle, and quarry floors are maintained parallel

L-HlS^iiliia^KSlgSi'KSS*

Fig. 42. — View from the bottom of a ^late quarry 450 feet deep at Pen Argyl, Pa.

of I ngersoll-Rand Company.)

{Courtesy

to it. Open seams and loose ribbons provide smooth, uniform quarry
walls in places.

Figure 42 illustrates a deep quarry in the Pen Argyl district. The
curved wall at the right resulted from the presence of a loose ribbon.

In 1929 five companies were operating near Windgap about 23^^ miles
southwest of Pen Argyl. The same beds as at Pen Argyl are present; and

248 THE STONE INDUSTRIES

conditions are similar, although each quarry has its own peculiar
structures.

Both roofing and mill stock are obtained from most of the quarries
throughout the Pen Argyl-Windgap district, and large, well-equipped
mills are associated with the quarries. Durable, unfading slates with
straight, easy cleavage are used for high-grade roofing material; rough
splitting slate and mill ends for heavy architectural roofing-slates; big
beds for blackboards and large slabs of clear structural slate; smaller
beds of high dielectric strength for panels and switchboards ; and ribboned
beds for various structural and sanitary applications. Granules and
slate flour are manufactured to a limited extent.

SLATiNGTON DISTRICT. — A westward extension of the soft-vein slate
beds has been quarried extensively in western Northampton County near
Berlinsville and across the Lehigh River in Lehigh County at Slatington,
Emerald, and Slatedale. The quarries near Slatington occupy an area
of about 3 square miles along Trout Creek and its tributaries. As in the
eastern Northampton County district, quarrymen give special names
to the commercial beds. Following the beds dow^nward — that is, from
north to south the following are recognized: Columbia, Manhattan,
Locke, Star, Keystone, Mammoth, Big Franklin, Little Franklin, Wash-
ington, Trout Creek, Blue Mountain, Saegersville, and Peach Bottom.

The "Franklin big bed" and "Washington big bed," as they are
sometimes termed, are the most widely known, as they provide clear
stock of high quality in large sizes. Some of the beds mentioned may be
duplications, for the folding is close, and the same bed could easily
reappear several times. Complete anticlines or synclines are observable
on some quarry walls, as the folding in this district is around axial planes
that stand more nearly vertical than at Bangor and Pen Argyl and have
the effect of repeating the outcrop of individual beds. The curvature
is plainly marked by ribbons. Slaty cleavage is quite steep, in many
places reaching 60 to 75°, though in some quarries it may be as low as
35°. Curved cleavage has been noted in some beds. The grain is
nearly vertical and at right angles to the cleavage. Joints or "headers"
dip at various angles. The rock is dark bluish gray, and most of it splits
easily. About 10 companies were active in the district in 1930. A great
many quarries have been worked, some of them to depths of 300 or more
feet, but most of them are now abandoned. Slate is being mined locally,
in addition to the usual quarry operations. Both roofing and mill stock
are produced by all the companies.

New Jersey. — An eastward extension of the Pennsylvania slate beds
crosses the Delaware River and extends into Sussex County, N. J., as far
as Lafayette and Newton. The deposit is regarded as a continuation of
the hard-vein slate occurring at Chapman Quarries and Belfast. Near
Lafayette, where commercial development has taken place, the beds dip

SLATE 249

about 18° northwest, while the slaty cleavage dips about 19° southeast.
The grain is vertical and at right angles to the strike of the beds. The
slate is blue-gray and intersected by numerous ribbons at 1- to 15-inch
intervals. Like the hard- vein ribbons of Pennsylvania, they resist
weathering.

For a number of years before 1918 roofing slate was produced from
a quarry about 11^ miles north of Lafayette. The quarry was reopened
in 1922 and again in 1928. Slate of high tensile strength, low porosity,
and attractive color is obtainable in this district, but economical operation
evidently has not yet been perfected, for activity ceased again in 1930.

Pennsylvania-Maryland. Peach Bottom District. — The slate belt of
the Peach Bottom district is one-fifth to one-half mile wide, extending
from about 1 mile northeast of the Susquehanna River in Fulton town-
ship, Lancaster County, Pa., southwest across the river, across Peach
Bottom township, York County, and continuing about 3 miles in Cardiff
township, Harford County, Md. Its total length is about 10 miles. For-
merly about 1}4 miles were beneath the Susquehanna River, but since
the Conowingo Dam was completed a larger part of it is submerged.
Quarries are situated near Delta, Pa., and Cardiff, Md.

The slate, bordered by schist, is regarded as of pre-Cambrian age and
overlies older gneisses and serpentine. Three parallel belts 75 to 120 feet
thick extend northeast-southwest, but their structural relations are
obscure. Slaty cleavage is uniformly vertical or dips at a steep angle.
One or more nearly horizontal joints pitching gently southward usually
are present 40 to 60 feet below the surface and known locally as "big flat
joints." They include 2 to 3 feet of crushed slate, the fracturing of which
has evidently resulted from secondary crustal movement. Commercial
slate occurs only below this joint. Other joints intersect the slate, some
being vertical and others dipping at various angles. Inclined joints,
with quartz veins and lenses, cause much waste. The grain dips 20 to 50°
northeast.

As recorded on page 237, the first slate quarry opened in America was
in the Peach Bottom district, and slate therefrom used on seven successive
roofs over a period of nearly 200 years is still in excellent condition.
Although Peach Bottom slate generally is recognized as of superior
quality, the industry has never flourished. Lack of activity is due to
unfavorable quarry conditions, which are discussed in a subsequent
section on quarry methods in the various districts.

Peach Bottom slate is dark bluish gray, with a lustrous cleavage
surface. It contains graphite, magnetite, and a little pyrite but is
notably free of carbonate. An unusual feature is the presence of numer-
ous small crystals of andalusite. The main product is roofing slate, which
has an excellent reputation. At times a small amount of structural
slate is made. Only two companies have produced during recent years.

250 THE STONE INDUSTRIES

Two large mills, one in Maryland and one in Pennsylvania, produce
granules and slate flour.

Virginia. Buckingham and Fluvanna Counties. — Slate extends from
Fluvanna County across the James River and southward over 5 miles.
From fossils found in the beds the rock is identified as of Ordovician age.
The slate occupies a zone about two fifths mile wide along Hunts Creek, a
southern tributary of Slate River. At Penlan it strikes N.30°E., at
Arvonia N.35°E., and on the north side of the James River 3}^ miles
north-northeast of Arvonia N.20°E. The best commercial slate occurs
near Arvonia in a belt 200 to 250 feet wide and about 1 mile long. To the
south of this area the slate is of good quality, but the belt becomes too
narrow for profitable mining; to the north, while the belt becomes wider,
the slate is poorer in quality and splits with greater difficulty.

Bedding dips southeast at steep angles of 80 to 85°. Slaty cleavage
parallels bedding. Vertical dip joints strike about northwest; other
joints run northeast and in diagonal directions. There are also gently
undulating "flat joints" which the grain parallels. Closed seams or
planes of weakness, known locally as "post," cross the deposit at 20- to
60-foot intervals and serve as headings for the benches. The post runs
diagonally, causing much waste in places. A diabase dike 7 feet across
was uncovered in opening a new quarry in 1930.

Nature has provided a very interesting index or guide to the best
commercial slates. A certain easily recognized bed serves as a reliable
marker in locating workable beds. This indicator bed is about 20 feet
wide and consists of characteristically spotted or pitted rock. It occurs
on the western side of the belt, and good slate always begins about
20 feet east of this bed.

Buckingham slate is very dark gray or slightly greenish, with a
lustrous surface. It contains a little graphite, magnetite, and pyrite
but is notably free of carbonate. It splits with difficulty, with a rough
surface, which is an asset according to modern architectural demands for
variegated texture. Virginia slate is so hard that channeling machines
can not be used, and quarrying is done by drilling and blasting. As
timed by the writer, a pneumatic drill bit 1 inch in diameter sinks at a
rate of only 2 inches a minute. Except for small quantities used locally
for monuments and a small but increasing amount for walks and terraces
the entire production is roofing slate. It is very durable and has a
splendid reputation. Slates from the roof of the McGuire residence in
Alexandria, Va., which was built in 1820, show no discoloration or sign of
deterioration. Three large companies were operating quarries in 1931.
The largest excavations are 500 to 600 feet long, 250 feet wide, and 200 to
225 feet deep.

Albemarle County. — The slate outcrop of Albemarle County lies east
of the Blue Ridge and 10 to 12 miles west of the Buckingham County

SLATE 251

belt. Quarries have been opened at Esmont on Ballinger Creek, a small
tributary of James River. The rock is intensely folded into a series of
synelines and anticlines. Slaty cleavage dips northeast at an angle of
70° to 80°. Discontinuous vertical joints strike N.58°W. and are spaced
2 to 10 feet apart. Close, irregular jointing causes much waste in the
upper levels. Both black and green slates occur, and the same beds
appear repeatedly on account of close folding. One opening has been
worked to a depth of about 200 feet. The slate is soft enough to permit
channeling machines to be used in the quarry and circular saws in the
mill. Both roofing slate and granules are produced.

During recent years roofing slate of good quality has been produced
at Monticello, but no details of structure have been obtained.

States of Minor Importance. — The following States have been inter-
mittent producers of slate on a small scale.

Arkansas. — The slate area of Arkansas extends about 100 miles west
from Little Rock nearly to Mena and has an average width of 15 miles.
The principal developments are near Norman and Slatington in Mont-
gomery County. The rock is compressed closely in overturned pitching
folds. In some places cleavage parallels bedding; in others it is oblique.
Both red and green sla.tes are obtainable, and near Mena, Polk County,
greenish gray and black slates occur. Many attempts have been made to
develop the Arkansas deposits, but none has been successful on account
of the distance from markets, high freight rates, and large proportion of
waste. Mill stock was produced years ago, but recent production has
been confined to a small amount of flagging for walks.

California. — Between 1889 and 1915, when activity practically
ceased, Eldorado County, Calif., produced considerable roofing slate,
attaining a maximum of 10,000 squares a year in 1903 and 1906. Quarry-
ing was conducted most actively near Kelsey. The slate which is of
Jurassic age is bordered by a large area of diabase. The bedding is
marked by numerous ribbons, which are generally within 10° of the plane
of slaty cleavage, the latter being practically vertical with a N.25°W.
strike. The ribbons are not of marketable quality. A series of joints
parallels the grain, which strikes N.55°E. and dips 70 to 80 northwest.
The rock is dark gray and resembles Pennsylvania slate in general
appearance. A 6-mile aerial tramway was employed to carry the product
to the railroad near Placerville. The Chili Bar quarry about 3 miles
north of Placerville has been worked intermittently for the production of
granules, and at times a similar product is produced in Tuolumne County.

Georgia. — The Rockmart formation of Polk County has been the most
productive slate belt of Georgia, yielding bluish gray roofing slate, with
some interruption, from 1880 to 1913, with a maximum output of 5,000
squares in 1894. The slate is of Ordovician age and is underlain with
limestone. Bedding strikes N.20°-40°E. and dips southeast about

252 THE STONE INDUSTRIES

20 to 25°. Slaty cleavage strikes with the bedding and dips 40 to 45°
southeast. Ribbons are spaced 2 to 5 feet apart in places, and joints are
15 to 18 feet apart. Decline of the industry is attributed to increasing
cost and unsystematic development.

A second slate district of Georgia is in the Conasauga formation
of Cambrian age. The best slate, which is greenish gray, occurs south
of Fair Mount, Bartow County. The beds are greatly folded and
contorted, with cleavage dipping 9 to 45°. A small amount of roofing
slate was made prior to 1913, but recent production has been confined to
green granules and slate flour.

Michigan. — A large deposit of black slate occurs at Arvon, Baraga
County, close to water transportation. More than 50,000 squares of
roofing slate were made before 1881, when the quarry was last worked.
According to report the slate is of good quality, but the industry failed
because of mismanagement.

Tennessee. — Purplish, greenish, and black slates, probably of Cam-
brian age, occur in Monroe County. Green slate has been quarried to
some extent near Tellico Plains for granule manufacture, but operations
were discontinued in 1928, and the plant was moved to Fair Mount, Ga.

Utah. — Green and purple slates occur in Slate Canyon about 2 miles
southeast of Provo station. Purple slates are more abundant and have
better cleavage than the green. Granules were produced in a small way
prior to 1922.

GENERAL PLAN OF QUARRYING

The economical development of deposits involves many complex
problems, because slate, having resulted from intense regional meta-
morphism, usually occurs in folded or steeply inclined strata. As pointed
out in the discussion of the origin of slate, the rock consisted originally
of clay deposited in horizontal beds on the sea floor. Materials forming
each distinct original bed were deposited under fairly similar conditions
and were uniform over wide areas. No matter how intense subsequent
metamorphism may have been, changes were usually the same within the
boundaries of each bed, and therefore slate as it appears today shows
remarkably constant quality throughout the extent of each bed.
Changes in thickness may occur as a result of folding, but from charac-
teristic qualities certain well-defined beds may be recognized at points
miles apart. Therefore, if high-quality slate is found in a certain bed
an operator plans his quarry to follow this bed. Knowledge of geological
structure is usually advantageous, as, for example, in regions where close
folding brings a desirable bed to the surface in a succession of outcrops,
where a pitching axis of a fold depresses a bed laterally below the limit of
economic recovery, or where a fault carries a bed beyond the boundaries
of a quarry.

SLATE 253

The plan of a quarry is governed chiefly by geologic structures. In
Northampton County, Pa., beds are marked clearly by ribbons and thus
are easy to trace. Bedding dips at steep angles, ranging from 70° to
vertical. Following desirable beds under such conditions carries quarries
down 500 to 700 feet. Such quarries may be worked for years, with
little expense for removal of overburden but with some attendant incon-
venience in access and hoisting. As the slaty cleavage is nearly horizontal
or dips at low angles quarry walls are very strong, with no apparent danger
of bulging or collapse even at the greatest depths to which quarries are
now worked.

In Maine the beds are narrow and vertical, and the cleavage is also
vertical, a condition which makes walls weak and in constant danger of
collapsing if open pits are sunk 200 feet or more. The necessity for deep
mining, combined with the inherent weakness in the walls, led to the
ingenious method of driving deep shafts with lateral tunnels and removing
rock by overhead stoping. Slate in the Peach Bottom district of Penn-
sylvania and Maryland likewise has vertical cleavage, but through lack
of foresight the weak walls were so overburdened with piles of waste that
very expensive slides resulted.

In Buckingham County, Va., bedding and cleavage stand at angles
approaching vertical, but cleavage is less perfect than in Pennsylvania or
Maine, and the effects of freezing and thawing are less severe. The
beds are thick enough to permit wide openings, and quarrying is not
conducted at excessive depths.

In the New York- Vermont area bedding dips at an average angle of
40 or 45°, ranging in different quarries from 15 to 60°. This condition
necessitates wide, comparatively shallow quarrying, for with vertical
descent a pit may pass entirely through the desirable beds. Further
development then demands extension along the strike. Extension of a
pit down the dip of beds requires removal of an increasingly heavy
overburden. Where beds are inclined moderately, underground methods
have been followed in a few quarries in Vermont and near Slatington, Pa.

Steeply inclined open joints and "loose ribbons" are structures that
demand careful attention, as they may endanger operations through slides
of rock masses left without support. Several quarries have been closed
because of such slides. A wise operator plans his quarry as a permanent
industry and at the outset maps a plan that will permit untrammeled
development indefinitely. Lack of capital has been the chief cause of
inadequate development of many slate quarries.

QUARRY OPERATIONS

Stripping. — Stripping methods are described in some detail in a
previous chapter. Where quarries are carried to great depths or where

254 THE STONE INDUSTRIES

underground operations are followed no stripping may be required for
10 to 20 years. It may become necessary at more frequent intervals in
regions where quarries are comparatively wide and shallow. A heavy
overburden of soil and decayed rock usually is handled by power shovels.
Removal of overburden to an insufficient distance has often necessitated
handling waste material a second time when workings are enlarged.
More progressive quarrymen transport overburden and waste far enough
to permit development for many years without rehandling.

Drilling. — Compressed-air, nonreciprocating, automatic rotation,
hollow-steel hammer drills are the most popular. In a few quarries
where no air compressor has been provided steam tripod drills are used.
Churn drills are employed occasionally where there is a depth of 20 to
50 feet of waste rock that requires heavy blasting for removal. Soft-vein
Pennsylvania slate may be drilled rapidly. A maximum of 240 feet of
drill hole per man during an eight-hour shift has been noted. The hard-
vein slate of Pennsylvania and the Virginia slate are drilled much more
slowly.

To avoid damage to good slate, drilling in the adjacent country rock
is sometimes necessary; and if such rock is highly sihceous, as in the
Maine deposits, drilling may be much slower than in pure slate.

Blasting. — Commonly 10 to 40, or even 50, feet of slate nearest the
surface is altered by ages of weathering and must be removed as waste
before merchantable rock beneath can be reached. Dynamite blasts in
tripod, hammer, or churn-drill holes are used to shatter the upper levels,
but heavy blasting close to sound slate is carefully avoided. Waste
immediately above good slate is commonly channeled, and then fractured
for removal with light charges of black blasting powder.

Black blasting pow'der always is employed in commercial slate, as
the higher grade explosives cause much waste. Very small charges may
be utilized to advantage in making cross fractures or floor breaks,
but in best practice drill holes for such shots are only three eighths to
five eighths inch in diameter; and it is customary, even when firing with
electricity, to place a length of fuse in a hole merely to take up space and
distribute a small charge throughout the length of the hole. Shots may
be fired with a fuse or by electricity.

Before channeling machines were introduced blasting was the chief
method of separating the larger blocks, and the method persists in regions
where the slate is regarded as too hard for profitable channeling or for
sawing with wire. In such quarries walls are rough and irregular, blocks
are rarely uniform or rectangular, and waste usually is excessive.

Wedging. — Wedges, used for making floor breaks in deposits where
quarry floors parallel cleavage, may be driven in drill holes or in notches
cut in the face. For subdividing larger masses the plug-and-feather
method described in a previous chapter generally is used. Wedging is

SLATE 255

much easier, and a smoother surface is obtained parallel to the grain than
in other directions.

Channeling. — Channeling machines are described in the chapter on
limestone. Steam-driven machines were introduced first in the slate
industry about 1897 and were superseded by compressed-air machines.
Channeling machines have been used widely in working the softer slates,
notably in Pennsylvania and in Maine, but have not been favored in
the New York-Vermont, the Peach Bottom, or the Virginia districts.
Their employment in the softer slates marked a great in^provement over
previous methods, but wire saws have rendered them obsolete except in
Maine quarries.

A machine known as a "bar channeler" or bar drill, previously
described in the chapter on granite, preceded the modern channeling
machine. It was introduced in slate quarries about 1887, but the process
was so slow that it was not used widely; however, the method has per-
sisted in some quarries where the "stunning" effect of channeling
machines causes excessive waste.

Cutting with Wire Saws. Early History. — Wire saws have been
used for many years in Europe for making long, deep cuts in slate, marble,
limestone, and travertine quarries, but until recently have been used to a
very limited extent in America. The only early record of successful
use in the United States concerns one marble quarry in Colorado where
about 1913 they were employed to cut
out a mass of marble between two
deep, open quarries. Their use as
yard equipment for trimming blocks fig. 43.— Details of steel wire used as

of limestone and marble is not Un- ''"re saw in quarrying, natural size, a,
, , . ,. , . 1 cross section.

common, but wire saws did not become

an essential part of any quarrying industry in American until general
acceptance in the slate quarries of Pennsylvania during the summer
of 1928.

Equipment and Method. — A wire saw is simply an adaptation by
modern machinery of one of the most ancient stone-working methods.
The man of the Stone age shaped his stone implements by abrasion or
grinding; a wire saw utilizes this same principle, as it cuts stone from its
original bed by a simple abrasive process. Sawing is done with a three-
strand steel cable three sixteenths or one fourth inch in diameter and 800
to 2,400 feet long, running as an endless belt. Wire of the smaller size is
illustrated in figure 43. Splicing requires skill and care, as the splice
must be strong enough to withstand heavy tension and also be smooth
and without enlargements. Any projection of the wire beyond the
standard diameter would bind in a cut, and the wire would be broken.
An 8- to 10-foot lap usually is provided in making a splice. Driving
equipment ordinarily consists of a 10-horsepower electric motor with

256

THE STONE INDUSTRIES

worm-gear reduction running in oil. The driving pulley is one double-
grooved cast-iron sheave, or a pair of single-grooved sheaves, 40 inches in
diameter. The wire passes from one groove to the tension pulley, back
to the second groove, and from there to the quarry where the slate is cut.
It travels at about 15 feet a second.

The tension equipment is a suspended platform on which a weight of
800 to 2,000 pounds is placed to give necessary tension to the wire.
The tension carriage may travel back and forth on a track; thus, the
necessary adjustment in length of the wire can be made as the cut pro-
gresses. The arrangement of driving and tension equipment is shown in
figure 44, A. Orienting pulleys mounted on standards conduct the wire
from the driving equipment to the cutting unit in the quarry.

Driving,
Unii- '

Fig. 44. — Diagram of wire saw. A, driving end; B, cutting end.

Equipment in the quarry includes a pair of angle-steel standards 14 to
18 feet long, each having one or two sheaves at the top for receiving and
conducting the wire to a lower sheave which travels up or down by a rope-
pull or chain-pull worm gear. An upper guide pulley is shown in figure
45. The standards, which usually are set 60 to 100 feet apart, are placed
either on platforms over the edges of open benches or in holes 10 to 14
feet deep and large enough to accommodate the movable sheaves. By
lowering the guide pulleys the wire is brought in contact with the slate
and when fed with sand and water it makes a cut over the entire distance
between the standards. The arrangement of the cutting equipment is
shown in figure 44, B. The original equipment had guide pulleys 26
inches in diameter, but 18- or 20-inch sheaves are satisfactory. The
heavy tension maintained on the wire prevents excessive upward curvature
of the cutting strands, making it possible to complete a cut with the
center not more than a few inches higher than the ends.

SLATE

257

Holes or open benches must be provided to accommodate the standards
carrying the movable guide pulleys, which descend as the cut progresses.
Where there are open benches platforms are secured to the wall of the
bench and the standards erected on the platforms. Where there are no
open benches a core drill making a 36-inch circular hole is used for
sinking holes in the rock. It consists essentially of a rotating notched-
steel drum 30 to 42 inches high to which steel shot are supplied as abrasive.
When the drum has cut to its full depth, it is elevated and moved laterally
to permit removal of the core; then it is again put in place, and another
section is cut. This process is repeated until a hole of the desired depth is
obtained. Holes may be vertical or inclined at any angle up to 45°,

Fig. 45. — Wire-saw standard and guide pulley; sand box in foreground.

although cutting is slower in inclined holes. Inclination is commonly
desirable to follow the direction of the ribbon so that the standards may
be similarly inclined, making the cut parallel the ribbon and thus reducing
waste. Sand and water are supplied through V-shaped boxes, as shown in
figure 45. Sand is carried into the cut by a small stream of water from a
rubber hose entering the upper end of the sand box. For a cut 80 to
100 feet long three or four sand boxes are used, one being placed as close
as possible to the point at which the wire enters the rock.

A sand box developed in the Indiana limestone district, where wire
saws are used for scabbling, consists of two compartments. One is
kept nearly full of sand, and a stream of water supplied to it overflows
through a hole into the second compartment, which contains water only.
A thick sand slurry is drawn off continuously through a spigot and
thinned to any desired consistency by the addition of a stream of water
from the second compartment.

258 THE STONE INDUSTRIES

With a cut 80 feet long in the soft-vein slate of Pennsylvania the
cutting rate is approximately 4 inches an hour. At this rate the guide
pulleys should be fed downward about 1 inch every 15 minutes. A
convenient measure of cutting accomplishment is the surface area obtained
by multiplying the length of a cut by its depth. Thus, a cut 80 feet long
and 10 feet deep provides 800 square feet of surface. Figure 46 shows the
lower sheave and the wire where it emerges from the cut.

Introduction of Wire Sawing in Pennsylvania. — The United States
Bureau of Mines, the National Slate Association, and a group of Penn-

FiG. 46. — Wire saw at the point where it leaves the cut.

sylvania slate producers cooperated late in 1926 in the purchase of wire-
saw equipment from a Belgian firm. The first cuts were completed early
in 1927, and the unqualified success attained led to its almost immediate
and general acceptance by the slate industry of Northampton County, Pa.
Within two years about 30 wire saws and 12 core drills were operating,
and work with channeling machines was practically abandoned. Many
improvements in equipment were worked out, and several American firms
undertook its manufacture. Its successful use in slate has led to its
introduction in some limestone and sandstone districts.

Cost of Cutting. — Few details of the cost of operating with wire saws
have been obtained. The records of one company provide fairly com-
plete figures for 11 months' operation of wire saws and core drill, although

SLATE 259

the labor had to be estimated in part, as it was diverted to other work
at times. During the period covered, 44 wire-saw cuts totahng 22,753
square feet of surface were made. As nearly as can be determined the
total cost, including labor, power, repairs, supplies, and interest on the
investment, was 14.3 cents a square foot. In making these 44 cuts, 35
core-drill holes were required. To obtain a figure comparable with
channeling-machine costs, the core-drilling cost for each square foot of
surface sawed, amounting to 10.1 cents, must be added, making a total
cutting cost of 24.4 cents a square foot. This record dated from the
beginning of operation of both the wire saw and the core drill. The
efficiency of new equipment of this character is very poor during the first
few months of operation; therefore, the cost figures given probably are
much higher than those obtainable toward the end of the 11-month
period.

Channeling-machine costs in the same quarry have been calculated in
two ways: (1) The average daily footage over a 5-month period was
divided into the total cost of channeling-machine operation, estimated at
$20 a day, giving a figure of 64.5 cents a square foot; (2) the actual
channeling-machine cutting in square feet was taken for a 19-day period,
and the total labor, supplies, repairs, power, and interest on the invest-
ment for that period were charged to it. Th'is method gave a cost of 73.1
cents a square foot. For the same footage, therefore, channeling-machine
costs in this particular quarry are two and one-half to three times as high
as wire-saw costs, even when the latter probably are materially higher
than the average costs under normal operating conditions with skilled
workers. A rate obtained by another quarry company was 18.9 cents a
square foot for wire saws compared with 50 to 70 cents for channeling.
Several years' experience by many operators has confirmed the early
favorable estimates and has firmly established the conviction that the
wire saw is the most economical means of cutting slate.

Advantages of Cutting with Wire. — Aside from the definite saving in
cost of operation, as previously mentioned, the wire saw has other
advantages, the most important being reduction in waste of rock. Search
for a practical means of reducing excessive waste was, in fact, the incen-
tive for the original experiments, and results have fully justified the effort.
In making a cut a wire saw removes about one ninth as much material as a
channeling machine, because a cut made with wire is only about }i
inch wide, whereas the width of a channel cut is 2'^i to 23^^ inches.
Still more important is the fact that a channeling machine wastes much
rock on either side of a cut through shattering or "stunning," but the
wire, cutting by simple abrasion, leaves the rock unimpaired. Formerly
many subdivisions into blocks were made by wedging along the grain or
sculp, and much stone was wasted because of irregularities in fractures.
Separation of blocks with wire results in smoother, straighter surfaces

260 THE STONE INDUSTRIES

with less waste. In some quarries the grain and ribbon meet at obUque
angles, commonly approaching 60°. By channeling parallel with the
ribbon and wedging on the grain angular blocks are obtained, and in
cutting them to cubical mill stock many triangular masses of good slate
are wasted. It is customary now to make wire-saw cuts parallel to and
at right angles to ribbons, thus producing right-angled blocks that are
utilized for mill-stock products, with a saving in stone of 10 to 15 per
cent over former methods.

It is difficult to determine accurately the saving of rock accomplished by
using a wire saw. No records of the gross tonnage of rock quarried have
been kept under either former or present conditions. Various operators
estimate a saving of 30 to 50 per cent. Other advantages are speed of
operation, adaptability for continuous work during day and night until a
cut is completed, simplicity and ease of operation, and ability to make
inclined cuts conform with ribbons or other rock structures. Through
this new method of making primary cuts, with consequent reduction in
cost of operation and better utilization of raw materials, an annual saving
to the Pennsylvania slate industry of at least a quarter of a million dollars
has been accomplished. Quarry methods have been revolutionized, and
the industry has been established on a more secure basis. Other slate
regions have been slow in following this lead, but experiments are contem-
plated, and after fair trial and patient effort to overcome the difficulties
peculiar to each deposit, definite success will no doubt be attained.

Floor Breaks. — Methods of separating masses of slate at the quarry
floor vary greatly, depending upon the structure of the rock. In Penn-
sylvania and in the New York- Vermont district, where slaty cleavage
dips 5 to 45°, a quarry floor is maintained parallel with cleavage, and
floor breaks are easily made by splitting in that direction. Notches are
cut in the face and wedges driven into them, a process known as "driving
up splits." For separating exceptionally large masses drill holes are
projected at the floor of the bench to parallel the slaty cleavage, and a
fracture is made by means of small charges of black blasting powder.
Where slaty cleavage is vertical or nearly so floor breaks are made with
greater difficulty. Wherever possible horizontal seams are utilized.

Subdivision of Blocks. — In quarries where the floor parallels slaty
cleavage most primary blocks are too large to be hoisted to the surface.
Subdivision parallel to cleavage is accomplished by cutting notches in
the face of the bench in a line parallel to the cleavage and about 18 inches
or 2 feet from the top of the bench. A split is made by driving wedges
in the notches. Longitudinal vertical fractures are made by drilling and
wedging in the direction of the grain. Breaks across the grain are made
in the same manner, but drill holes must be closer together than where
they are parallel with the grain.

Block Raising. — After a block of the desired size is broken loose,
several men working simultaneously raise it by heavy bars with curved

SLATE 261

ends, used as levers. Freeing the rock is sometimes slow and difficult,
not only because of its weight but because of many interlocking corners
that must be actually broken. The most effective work results when
the energies of all the men are applied to their bars at exactly the same
moment. To obtain such unanimity a foreman frequently leads in a
sing-song rhyme, the men joining and keeping perfect time with their
crowbars. When a block is raised sufficiently a fragment of stone or a
wedge is dropped in the crack, the bars are placed in more advantageous
positions, and the process is continued until a hoist chain can be passed
under the block.

Hoisting. — Wooden derricks and compressed-air hoisting engines
are used in the Monson (Me.) district, but in practically all other districts
overhead cableway hoists are employed. Derricks may be advantageous
where a quarry is small or where, as in Maine, rock is removed from deep,
narrow quarries or from mine shafts. In most regions, however, pits
are so wide that a derrick boom can not reach all parts. For large pits
three to six parallel cableways are commonly required to serve properly
all parts of an excavation. The main cables range in diameter from 13^^
to 2)^^ inches, and the draw cables from 3^ to % inch. Most of them
are designed to carry 3 to 5 tons. Cable spans between supports (wooden
or structural steel masts) range from 500 to 1,800 feet. An advantage of
the cableway system at many quarries is its ability to convey waste rock
to the spoil bank by a single handling. Carriages equipped with auto-
matic dumping devices are widely used. Supplementary derricks are
used at some quarries for hoisting from pits or for yard service.

Signaling is usually done from a small house known as a "motion
shanty," which overhangs the brink of a pit in such a position that a
signal man has a clear view of the entire quarry floor. (See fig. 42.)
By means of an electric button for each cableway the signal man sends
to hoist engineers the messages which control all hoisting in the quarry.
At some quarries, particularly in the Vermont-New York district, a
board arm is used in place of electric devices. A board about 2)-^ feet
long and 5 or 6 inches wide, pivoted near one end, is attached to the roof
of the motion shanty and moved by a wire leading inside. The signal
code is based on the motions of the board.

The only means workmen have of entering or leaving the deeper
quarries is by cableway pan. A special signal is given when men rather
than materials are being conveyed, so that hoist engineers may exercise
special care. Hoisting accidents rarely occur.

QUARRY METHODS

Influence of Rock Structures. — The various processes by which
blocks of slate are separated from their original beds and hoisted to the
surface are covered in preceding paragraphs. There are many variations
in the manner in which these processes are combined, and differences in

262

THE STONE INDUSTRIES

method depend chiefly on rock structures. Ease of sphtting, direction
of slaty cleavage, direction of grain, position of joints, and dip of beds
influence the method. Slate can not be quarried successfully without
detailed knowledge of these physical properties, and familiarity with them
is gained only by actually working with the rock for some time. A
quarryman learns to know his rock, and this knowledge guides him in his
choice of methods. Quarry methods in their relation to rock structures
in each of the principal producing districts are covered in following pages.
Pen Argyl-Bangor District. — The slate area of eastern Northampton
County includes quarries in and about Windgap, Pen Argyl, Bangor,
North Bangor, and East Bangor. The output of this region exceeds that
of any other slate district in the United States.

Fig. 47. — Rock structures and quarry plan at a typical Pen Argyl, Pa., slate quarry,
a, direction of grain; b, ribbon; c, direction of dip of slaty cleavage; d, "loose ribbon;" r,
drainage sump; /, mass of slate ready for floor break; g, h, drill holes for "scallop" or
"sculp" blasting.

The strike of the rock is in general east-west but differs considerably
in different quarries. The structural feature that has greatest effect on
the quarry plan is the steep dip of beds, as indicated by ribbons. In
several deep quarries the ribbon is vertical or curves back and forth
from north to south in gentle, sweeping folds, usually at steep angles,
though in some quarries at East Bangor it dips only 30 to 40°. In
general, however, beds are so nearly vertical that the region is character-
ized by deep quarries with vertical or nearly vertical walls. Loose
ribbons and open joints may commonly be utilized to take the place of
channel or wire-saw cuts. Joints are generally spaced to permit removal
of large blocks.

A second structural feature which is decidedly favorable is a slaty
cleavage dipping at low angles, ranging from 5 to 30°. Quarry floors are
maintained parallel to cleavage; thus, blocks are easily separated, and
most of the floors are flat enough to be worked conveniently.

The positions of ribbon and grain govern the direction of cuts in a
quarry. In some quarries they intersect at nearly right angles; in others,
at angles of 70 or 80°. Before wire saws were introduced it was customary
to channel parallel to the ribbon and to make cross breaks parallel the
grain, either by wedging in drill holes or by using light charges of black

SLATE

263

Fig. 48. — Method of cutting a channel in
which standards are placed for transverse
cuts, a, core drill holes; b, wire saw cuts to
make channel; c, subsequent transverse wire
saw cuts.

blasting powder. This resulted in the production of angular blocks, as
indicated in figure 47, and in cutting such blocks into right-angled mill
stock the waste was excessive. Since wire saws have been used it is
customary to make cuts parallel to and at right angles to ribbons, produc-
ing rectangular blocks that may be cut advantageously into structural
products. However, for roofing manufacture angular blocks commonly
are used because there is less waste in reducing them to thin roofing than
in cutting them into slabs or cubical stock.

In opening up a new floor with wire saws core-drill holes are sunk in
the corners of the quarry, and from them wall cuts may be made in two
directions at right angles. Core
drilling is slow and expensive,
therefore operators usually plan
to utilize the holes to best advan-
tage. Where a series of parallel
cuts is to be made four holes may
be drilled, as shown diagram-
matically in figure 48. Wire-saw
cuts are made as indicated at b,
and the slate lying between them
is removed. A trench is thus
formed in which a standard may be
placed in any desired position for making the subsequent cuts, c.

A wire-saw cut is only one fourth inch wide, and blocks may jam in
relnoval if proper precautions are not taken when a new bench is opened.
To facilitate removal of key blocks cuts are not made parallel but con-
verge, as shown in figure 48. Binding is avoided by removing blocks first
at the wider end of the wedge-shaped mass. The cuts also are inclined
slightly toward each other, so that the mass of rock between is narrower
at the bottom than at the top; then, as wedges are driven and blocks
lifted the wider space in the upper levels provides ample room for any
necessary lateral movement.

The advantages to be gained from wire saws are now generally
recognized, and they are widely used to make numerous parallel cuts
whereby slate is obtained in smooth, rectangular blocks. Operators are
beginning to realize the advantage of numerous cuts; consequently, the
general appearance of quarries is markedly changed. Instead of curved,
irregularly broken bench walls, floors rise from bench to bench in regular
steps resembling those of a marble quarry. Wire-saw equipment in
process of making a cut 80 feet long is shown in the center of figure 49.
The walls at the upper left corner were cut with wires.

Slatington District. — The Slatington district, comprising the quarries
of Lehigh and eastern Northampton Counties, Pa., is characterized by a
series of close folds with east and west axes that pitch east. The ribbon

264

THE STONE INDUSTRIES

is distinct, and many loose ribbons or open bedding planes greatly facilitate
quarrying. Because of the close, repeated folding quarrying is complex,
and an operator must have a clear idea of the rock folds in and about his
quarry to develop the slate to best advantage. A succession of folds
may cause a bed of high-grade slate to reach or approach the surface in
several places. Probably in some quarries what has been regarded as a
succession of good beds is merely a single bed brought to the surface by
repeated folding. Some quarries are on synclines and others on anticlines ;
still others are worked on single limbs of large folds.

Fig. 49. — A Pennsylvania slate quarry, illustrating method of developing a new bench
with wire saws; standard holding guide pulleys in foreground. {Courtesy of I nger soil-Rand
Company.)

A remarkable feature of the Slatington district is the uniform dip of
slaty cleavage. With few exceptions, it dips 60 to 75° south, irrespective
of the folding of the beds. The sculp or grain is also remarkably constant,
crossing the rock generally a little east of south, and dipping to the east
at a steep angle, approximately 85 to 88° from the horizontal. Hence,
following the sculp tends slightly to undercut the east walls of quarries.

Joints and loose ribbons are utilized for headings and bench floors.
If no open seam or ribbon is available floor breaks must be made in the
hard-way direction, which gives rough, uneven floors. The downward
curvature of a high-grade big bed under a great thickness of waste rock

SLATE

265

has led to the development of underground methods. One quarry near
Berlinsville has quite extensive underground workings.

Hard -vein District. — Structures of the hard-vein slate at Chapman
Quarries and Belfast, Pa., are similar to those in the soft vein of eastern
Northampton County. Slaty cleavage dips 5 to 15°, and quarry floors
are maintained parallel with it. Wire saws are used successfully,
although the rate of sawing is somewhat slower than in the softer slates.
A vertical grain is utilized in making cross fractures.

Granville -Fair Haven District. — In Washington County, N. Y., and
Rutland County, Vt., the slates dip at angles approaching 45°. Quarries
are relatively shallow because the depth of overburden becomes very

Fig. 50. — Rock structures and method of separating blocks in a quarry near Fair
Haven, Vt. o, grain direction; b, open bedding planes; c, split holes; d, notches for wedging;
e, break on grain;/, break across grain; g, dip of beds and slaty cleavage.

heavy in following down the dip. In some workings near West Pawlet,
however, the beds dip steeply, and quarries are deep. Slaty cleavage is
at steeper angles than in Northampton County, Pa., ranging from 10 to
30°. Quarry floors parallel the cleavage and are inconveniently steep
in some quarries. Channeling machines are not used in this territory,
as it is claimed that the rock is too hard for successful operation. Vertical
joints are utilized wherever possible for walls and bench headings. If
joints are not available fractures are made with charges of black blasting
powder. Rock structures and methods in a typical quarry of this
district are shown in figure 50.

Open beds, as indicated at b, commonly occur at intervals of 5 to 7
feet and are thus spaced conveniently for bench floors. Cleavage par-
allels bedding. If a floor is tight, holes are drilled along the bed from the
open side, as shown at c, and very light charges of black blasting powder

266 THE STONE INDUSTRIES

are fired in them to jar the rock and free the bed. When the floor is free,
a break is made on the grain by blasting in holes drilled the full depth of
the bed. One hole is made for about each 15 feet of the desired break.
"Foot joints" or "headers" are commonly utihzed to form the third
free face, but if they are not available, blasting is used. Large masses
are thus set free, and further subdivision is made first by driving wedges
in notches cut in the face, as shown at d, and then by using plugs and
feathers in drill holes parallel to and across the grain, as shown at e and /.
In some quarries in the southern part of the slate area the dip of beds
and cleavage approaches 60 or 70°; consequently, underground methods
have been followed. Webs or elongated pillars of slate are left at intervals
to support the steep, overhanging roof.

Overhead cableway hoists are used almost universally. Roofing

slate is manufactured at the quarries,
although mills for structural and electrical
slate usually are situated at near-by towns.
Peach Bottom District. — Although Peach
Bottom slate has a nation-wide reputation
for high quality, in some respects quarry
conditions are unfavorable. In a number
of quarries steeply inclined open joints
have permitted unsupported masses of rock
to slide into the pits. The tendency toward
driff f» 'leThlrSpSl'Mon- wall collapse is increased through the pres-
son, Me. a, drift; ?>, 10-foot slate ence of a vertical cleavage which weakens
'if^bed^rVpefventaurms'; walls and makes them incapable of support-
/, horizontal roof seam; g, drill ing heavy loads. Channeling machines are
holes for blasting. ^^^ ^^^^^ p^^^j^ ^ecause the vertical

cleavage is unfavorable and partly because the rock is considered too
hard. Benches are worked to open joints wherever possible. If no
flat joints occur floor breaks must be made by blasting across the cleavage.
Monson District. — Conditions at Monson, Me., are similar to those
in the Peach Bottom area, except that the best beds are relatively thin.
Both bedding and slaty cleavage are vertical, and much of the highest-
grade slate is obtained from one 10-foot bed. Deep quarrying in narrow
opencuts was beset with many difficulties, owing to bulging or collapse of
the walls. Cross supports, consisting of steel I-beams and concrete, were
constructed at great expense in an effort to hold the walls apart, but at
depths beyond 300 feet they were inadequate. An overhead-stoping
system was then introduced and has been very successful. The first
step was to project drifts right and left at the old quarry floors about 300
feet below the surface. They were driven 80 to 100 feet along the slate
bed, and vertical wall seams and horizontal floor and roof seams were of
great assistance. The procedure when a drift is completed is shown

f J

0
0

9°

SLATE 267

in figure 51. At the northwest side of the drift, or at the left, as shown in
the figure, a 2-foot slate bed, c, is separated by a few inches of quartzite,
d, from the 10-foot slate bed, h. Good slate could be obtained from the
2-foot bed, but as the slate drills much more easily and rapidly than the
quartzite, holes are drilled in the narrow bed, which is largely destroyed
in quarrying. Drills are mounted on scaffolds and holes laid out on 16-
inch centers and staggered, as shown at g in the figure. The depth of
holes is governed by the position of the back seam, but it averages about
12 feet. The holes are loaded with light charges of black blasting
powder and fired singly, beginning at the lowest. They are staggered to
prevent the discharge of explosive in one hole from shattering the rock
surrounding the succeeding hole. The narrow band of quartzite serves
as a cushion and prevents shattering of good slate in the 10-foot bed. A
mass of stone is worked down in this way until an upper seam is reached,
as shown at / in the figure ; then a final shot is discharged in a vertical
hole drilled in the back corner at the southeast side to clear down all the
slate to the open seam. From the mass of stone thus thrown down all
good material is selected, hauled to the drift entrance by cable, and
lifted to the surface by derrick hoists. Waste slate is left on the floor,
and the heavy cost of removal is thereby saved. Thus, the floor is
constantly built up with waste; for ideal operation it should keep pace
with the upward progress of stoping from the roof. Waste is not suffi-
cient in volume to build up the floor as fast as the roof is elevated, and
additional rock is blasted from drift walls to keep it within easy reach of
the roof. The drift is gradually worked upward toward the surface.

The method proved so successful that one company put down a shaft
1,000 feet deep and drove lateral tunnels from its bottom. Thus, a
reserve of slate is provided for many years' constant mining. Advantages
of the stoping method are: (1) The great saving occasioned by leaving
waste rock in the pit; (2) reduction in hazard from roof falls, as the floor is
at all times only a short distance below the roof; (3) reduction in hazard
from fragments of falling rock during hoisting or from falls of rock from
walls or upper edge of excavation; (4) elimination of impediment to opera-
tion from snow, ice, or inclement weather; (5) absence of danger from
collapsing walls.

Where a series of many parallel slate beds is worked open-pit methods
are followed. Channeling machines are used, but they cut rather slowly
on "edge-grain" rock.

Arvonia District. — Slate structures of Buckingham County, Va., are
similar to those in the Peach Bottom and Monson districts, in that bedding
and slaty cleavage are nearly vertical, ranging from 80 to 85°. Open-pit
methods are employed, and some quarries reach a depth of 225 feet.
Walls are quite secure, with no apparent danger of collapse. Buckingham
slate is so hard that no successful means of cutting it has yet been found.

268 THE STONE INDUSTRIES

In opening a new floor a trench 6 to 10 feet wide and 12 feet deep is first
made, usually in a zone of defective rock, as the heavy blasting required
would destroy good slate. Benches are always terminated at closed
seams or "post," along which the rock breaks easily. From the bottom of
the trench horizontal holes are drilled about 12 feet deep, and about 12
feet back from the edge of the trench steeply inclined holes are sunk
parallel to the slaty cleavage. Vertical holes are drilled also along
the "post." Black blasting-powder charges are fired simultaneously
in all the holes, and thus a mass of slate is broken loose. A disadvan-
tage of the method is fracturing in three planes simultaneously, which
shatters the slate excessively. According to best quarry practice a
fracture should be made by blasting only when there are five free faces
instead of three.

YARD TRANSPORTATION

Slate blocks transported to quarry banks by cableways usually are
placed on small cars and conveyed to splitting sheds or mills for treat-
ment. For this haulage, gasoline locomotives are popular. Sometimes
finishing mills are located in towns several miles distant from quarries,
necessitating transportation by motor trucks or other means.

An important part of yard transportation is involved in the disposal
of waste rock. Tracks from quarry banks usually lead by a moderate to
steep incline over a waste heap, which gradually increases in height and
in lateral extent as cars loaded with waste are hauled by cable and
dumped at the end of the track. In some instances quarry waste is
conveyed directly by overhead cableways, and if an automatic trip is
provided no labor is required for disposal.

Transportation also involves conveyance of finished products to
railway sidings or storage yards. As roofing slates often are split at
shanties on high waste heaps the slates are conveyed down to the normal
ground level by cable cars. For this purpose long eight-wheel cars
commonly are used. In many places where transportation lines are not
immediately available teams and wagons or motor trucks are used for
both short and long hauls.

A unique method of transporting slate from quarry to railway is an
electrically driven aerial tramway 2 miles long at South Poultney, Vt.
It carries 400 buckets and has a capacity of about 200 squares a day.
Two men load and three unload the buckets.

MANUFACTURE OF ROOFING SLATE

The manufacture of roofing slate is the oldest branch of the industry,
and, strangely enough, the essential processes of splitting and trimming
are conducted in the same way as when the industry was in its infancy.
Many years ago a slate-splitting machine was invented and used success-

SLATE 269

fully in an experimental way, but never for commercial production.
This machine split the slate by rapid impact of a flexible steel blade.

Shanty Method. — What is known as the "shanty method" of making
slate dates back to the beginning of the industry and is still widely used.
Quarry blocks of suitable slate are conveyed directly to splitting shanties,
which usually are high on waste heaps. The shanties are only large
enough to accommodate two men — a splitter and a trimmer — and are
heated in winter by small coal stoves.

The first process is known as "block making," a reduction of large
masses to sizes suitable for splitting. Blocks are split to any desired
thickness by driving wedges in the direction of slaty cleavage. They are
then "scalloped" longitudinally in the grain direction by wedging in
plug holes.

Intimate knowledge of the physical properties of slate is essential in
breaking and splitting blocks properly. A skilled slate worker drives a
wedge or plug until a strain is placed on the rock; he then procures a
straight break by striking a blow with a wooden sledge at a particular
point on the rock ; he can thus within certain limits force a fracture where
desired. The slate is split on the grain into masses about 14 to 24 inches
wide, and these are then broken across.

Various methods are used to subdivide slate masses across the grain.
The corners may be notched with a chisel or with a small saw and a
smooth, even break obtained by striking one or two heavy blows with a
large wooden mallet. To cushion the blow and thus preserve the slate
from damage a thin flake of slate or a handful of fine slate rubbish
usually is placed on the surface of the rock where the mallet strikes.
Slates that break with difficulty may be sawed across with circular saws.

After they are broken across the cleavage the masses of slate are
split parallel to the cleavage with a hammer and special chisel known as a
"splitter"; the thicknesses thus produced are sufficient for eight slates
each. The thickness of a slab is always measured with the splitter.
Thus, if a thickness of %6 iiich is required for the finished slate, the
splitter blade is eight times ^e inch, or 1}^ inches wide; if the thickness is
to be increased slightly the blacksmith is instructed to make the splitters a
little wider.

Blocks are not allowed to dry out until finally made into roofing
slates, as they split with much greater ease if the quarry sap is not allowed
to evaporate. Maine slates are said to be an exception to this rule, as
they split readily when dry. Blocks are made in the yard and finished
blocks piled in the shanty. Here a slate splitter sits on a low seat with a
block of slate resting against his knee. His tools are a wide, flexible,
splitting chisel and wooden mallet. Blocks always are split in the center
until slates of finished thickness are obtained. Some slates are split
from the ends of the blocks and others from the sides. For tough-

270 THE STONE INDUSTRIES

splitting slate the chisel may be greased. A pneumatic chisel that has
been used successfully in Vermont is impelled by rapid vibrations on the
same principle as a pneumatic drill or stone-dressing tool.

A trimmer takes the slabs from a splitter and cuts them rectangular.
The trimming equipment most often used, particularly in Pennsylvania,
is a straight blade about 3 feet long, run by a foot treadle. The outer
end of the blade is attached to an overhead spring pole, so that the
blade strikes repeated blows when once set in motion by the treadle.
Another common type is a rotary trimmer which has a curved blade
similar to the cutting blade of a lawn mower. Most trimmers of this
type are run by foot treadles, though at some plants they are belt-driven
from a countershaft.

The steel gage bar on which slates rest for trimming has a series of
notches which serve as guides in trimming to standard sizes. A skilled
trimmer can determine very quickly the size to which each slate will
trim to best advantage. The following table shows the standard sizes,
in inches, of roofing slates carried in stock by most companies:

Slate Sizes for Sloping Roofs

10 X

14 X 9

18 X 12

10 X

14 X 10

20 X 10

10 X

14 X 12

20 X 11

12 X

16 X 8

20 X 12

12 X

16 X 9

20 X 14

12 X

16 X 10

22 X 11

12 X

16 X 12

22 X 12

12 X

18 X 9

22 X 14

14 X

18 X 10

24 X 12

14 X

18 X 11

24 X 14

Slate Sizes for Flat Roofs*

6 X

10 X 6

12 X 6

6 X

10 X 7

12 X 7

6 X

10 X 8

12 X 8

3 for ordinal

•y service usually are ^ie

inch thick.

For promen;

ordinary service they may be }'i to ?^ inch thick.

To facilitate handling roofing slates racks with a series of shelves
divided into compartments are provided within easy reach of the trimmer.
Slates are sorted according to size and quality as they are made, and a
section is reserved for each class. Once a day, either just before closing
time or early in the morning, the slates are loaded on cars and taken to the
piling yards. A typical roofing-slate piling yard is shown in figure 52.

Mill Method. — One efficiently planned roofing-slate mill has been
operating for many years near Poultney, Vt. About 1925 several com-
panies in Pennsylvania erected and equipped mills for the same purpose.
A plan of a typical mill is shown in figure 53. Blocks are brought into
the mill on cars and stored at c. The mills are equipped with overhead
traveling cranes or derrick hoists. Slate blocks are cut to desired

SLATE

271

lengths with circular saws. By using saws objectionable "ribbons" or
" hard ends " may be cut off, and thus many blocks which would be thrown
away by the old method may be used. A saw cut provides a smooth
surface, which makes splitting easier and also tends to conserve slate,
for it is straight, while the breaking method often results in crooked and
uneven fractures. One company has equipped its mill with a 60-inch
diamond saw for cross cutting blocks of "hard-vein" slate. It is claimed
that waste is reduced at least 15 per cent thereby, and mill production
per man is increased a like amount. In mills one blockmaker and
helper can provide blocks for two splitters. By the shanty method a
splitter spends part of his time making blocks, piling slates, or shoveling
rubbish; by the mill method he splits practically all the time. All

Fig. 52. — Typical roofing-slate piling yard with splitting shanties in background.

trimming machines in mills are power-driven; thus, the tiring operation
of a foot treadle is avoided. Also, finished slates are piled in portable
racks mounted on wheels. The filled racks are hauled to the storage
yard by gasoline locomotive, horse, or other means. Thus, arduous
rehandling of slate is avoided. Waste from both trimmer and splitter
falls down slides into cars on depressed tracks and is conveyed to a dump,
or it may be carried continuously with a belt conveyor.

"Architectural" Slates. — The preceding paragraphs on roofing slate
deal exclusively with standard types three sixteenths to one fourth inch
in thickness. Until recent years only smooth slates of uniform size and
color have been in demand, but modern architectural taste calls for
increasing quantities of rough-textured slates, graded in size and of vari-
able and mottled colors. Slates showing contrasting color effects are
obtained mainly in the New York- Vermont district, but many textural or
"architectural grades" are produced in other districts. Variations in

272

THE STONE INDUSTRIES

-I—

e
7

e
7
e
7
e
7
e

TFT

Fig. 53. — Plan of roofing slate mill, a, track for slate blocks
block storage; e, saw beds; /, boxes for waste; g, blockmakers; h,
belt conveyor for waste; I, track for portable slate rocks; m, track

; h, traveling crane; c, d,
splitters; z, trimmers; k,
for waste.

SLATE 273

sizes, colors, and surface finish produce rustic effects that are very attrac-
tive, particularly in large structures. The demand for slate of this type
has been advantageous to producers. No substitute materials have been
found that provide the rustic effects of the natural slates, and therefore
this branch of the industry has grown rapidly. Furthermore, large,
heavy slates, some of them 1 to 2 inches thick, may be manufactured
from beds where the material has too poor a cleavage for manufacture
into standard-grade roofing slate, and more complete utilization of quarry
rock is possible. Special types of powerful trimming machines are
employed to dress massive slates. The knives are constructed purposely
to make wavy, irregular outlines.

STORAGE OF ROOFING SLATE

Finished slates are piled on edge in storage yards, and each pile
comprises slates of the same size. They are placed in a nearly vertical
position and usually are stacked not more than three tiers high (see
figure 52). As a rule, slates are punched for nailing before shipment.
A punching machine, operated by a foot treadle or motor, punches two
holes simultaneously. The side uppermost in punching is placed down-
ward on the roof, for the punch makes an inverted conical hole, the
larger part of which provides a ready means of countersinking a nail
head. Slate too thick to punch and some thin slates on special orders
are drilled and countersunk, usually with motor-driven rotary drills.

THE ART OF ROOFING WITH SLATE

To endure for many years a slate roof must consist of high-grade
material free from cracks or other defects. The units must be of standard
thickness and proper manufacture, with the grain parallel to the long axis.
Part of the responsibility for a good roof rests however with the roofer,
for excellent-quality slate may make a leaky roof if improperly placed.
That any carpenter can lay slate is a common statement, and many roofs
are laid by inexperienced workmen, but they give much better service
when placed by men who specialize in such work. For example, in
placing slates most carpenters drive the nails "home," just as they would
in securing wooden shingles, with the result that if the sheeting dries
and shrinks the slates are cracked. A skilled slate roofer does not drive
the nail to its full depth, but allows the slate to hang loosely.

Another common error is due to mistaken economy or even dis-
honesty on the part of a roofer who to save slates may give a head lap less
than the regulation requirement of 3 inches. As a result the roof may
leak, not through any fault of the material, but because of improper
workmanship. The law in some States renders it illegal to place slate
with less than a 3-inch head lap. Nails and other metal work used in
conjunction with slate should be durable.

274 THE STONE INDUSTRIES

MANUFACTURE OF SCHOOL SLATES

Slate suitable for the manufacture of school slates is found in soft,
black beds free of all hard streaks or knots of flinty material. The
rough blocks are split in the same manner as roofing slates, but trimming
is done with small saws rotating at high speed. The shape of one type in
common use is shown in figure 54. When trimmed to size they are

delivered to school-slate factories. Here
the edges are first beveled; then the
slate is placed on edge between two
knives, and a descending bar forces it
down, so that the knives scrape off all
rough projections. A second pair of
knives gives a smoother surface. The
slates are then polished between sanded
drums, thoroughly washed in hot water,
and carried on a belt conveyor through
a heated chamber for drying before being
piled. They are then ready for framing.
Fig. 54.— Type of rotary saw used for gjates broken in framing are unframed

trimming school slates. n . ci i

and recut to smaller sizes, iseveral
million school slates are manufactured in the United States every year,
and about 90 per cent are exported.

MANUFACTURE OF MILL STOCK

The term "mill stock" includes all forms of structural slate, such as
steps, wainscoting, baseboard, lavatory enclosures, and mausoleum
crypts, as well as billiard tables, grave vaults, blackboards, and electrical
panels or switchboards. The chief processes within the mill are hoisting,
sawing, planing, edging or jointing, rubbing, and buffing or polishing.
Mills usually are close to quarries and are in the form of long closed
sheds. Slate blocks are brought from quarries on cars hauled by gasoline
locomotive or some other means. Derricks are provided for handling
blocks and waste, but some newer mills have overhead traveling cranes of
5- to 10-ton capacity.

Sawing. — Quarry blocks are measured and marked in accordance
with the products to which they will cut to best advantage. A marked
block is placed on a saw bed, which is propelled back and forth by a
pinion working in a rack of cogs. Different rates of travel are made
possible by a system of gears. The slow speed may be not more than
3 inches a minute ; when thinner or softer slate is cut a bed may travel 20
inches a minute or faster. The belt which drives the saw runs on a
cone of pulleys; thus different rates of rotation may be obtained, and the
desired speed is governed by the nature of a slate block. An average

SLATE 276

rate is six or seven revolutions a minute. Saws range from 24 to 48
inches in diameter and are about % inch thick. The teeth are so widened
that a saw makes a cut about ^i inch wide. Ordinarily the saw tooth is
part of the blade, but an inserted tooth saw is used where flint knots or
pyrite crystals are liable to break teeth. Some experimental work has
been done with tungsten carbide-tipped teeth, but such saws are not
yet used commercially.

Gang saws are employed to a limited extent in Vermont in slate
regarded too hard for circular saws. They are the same in principle as
gangs described in the chapter on limestone, except that the blades are
only about 6 feet long. Steel shot are used as abrasive.

Experiments are contemplated with the view of adapting wire saws
for reducing mill blocks.

Disposal of Sawed Blocks. — After sawing is completed the next step
in manufacture depends upon the purpose for which the slate is to be
used. When clear blackboard stock is obtained the block is hoisted
from the saw bed and leaned against a wooden or concrete pedestal.
With hammer and thin flexible steel chisels it is split into slabs about
one half inch thick. Slate with a straight split is in great demand, for if a
curved or twisted surface is obtained the finishing process is expensive,
as much slate must be worn away to reduce the surface to a perfectly
uniform plane. Finishing processes are described in later paragraphs.
For other forms of mill stock, sawed blocks are split to approximate
thicknesses desired and placed on planer beds.

Surface Finishing. — Planing is the first step in surface finishing.
The tool — a heavy blade set horizontally and adjustable laterally and
vertically — planes the surface of a block as it is carried back and forth on a
traveling bed. With each motion the tool is moved laterally until it has
passed over the entire surface. If all irregularities are not removed the
tool is set at a lower level and the block replaned. It is then turned over
so that the smooth surface rests on the bed, and the opposite side is
planed in the same manner, but special care must be taken to obtain the
desired thickness for the finished product. A block is not reduced to its
final thickness in a planer, for some allowance must be made for removing
slate during subsequent processes, such as rubbing or honing. Black-
boards are planed only when they are uneven or have a curved split.
For rougher forms of structural slate, such as grave vaults, planing gives
the final surface finish.

For a smoother finish slabs are placed on rubbing beds similar to those
used in marble and sandstone mills. They consist of cast-iron disks
12 or 14 feet in diameter which rotate in a horizontal plane with the slate
slabs resting on the upper surface. A stream of water is constantly
supplied, and sand is used as abrasive. A rubbing bed is not only used to
obtain a smooth surface but also to grind rectangular blocks to size. An

276 THE STONE INDUSTRIES

operator uses a gage and square and thus can turn out blocks true to
size and having right angles. A rubbing bed also is used for making
beveled edges on switchboards and other products, though often a coarse
file, pneumatic tool, or Carborundum wheel is used for this purpose.

Certain products, such as blackboards and switchboards, require a
much smoother finish than is obtainable on a rubbing bed. A fine polish
or honed finish may be obtained with a belt or drum sander, a buffer,
some other form of polishing machine, or by hand. A buffer, which is
most commonly used, consists of two movable arms; one attached to the
end of the other, holding a rotating buffer head. The latter is belt-
driven, with one belt for each arm, and the pulleys are so adjusted that
their axes coincide with the axes of rotation of the arms ; thus, the polishing
head may be moved about to any desired position without interfering in
any way with the movement of belts. The rotating head is fitted with a
set of six or seven blocks set in plaster of paris and consisting of polishing
materials made up in accordance with various formulas worked out by
mill operators. A stream of water is directed on the surface, and the
rotating head is moved back and forth until a fine polish is obtained. A
special type of multiple-head polishing machine, consisting of a series of
six rotating arms, each with a polishing block, has been devised to take
the place of a buffer. The circles overlap, and the arms are so adjusted
that blocks follow each other over the same ground with no interference.
A slab of slate to be polished is placed on a traveling bed which conveys it
back and forth beneath the rotating arms. In some mills blackboards are
finished by hand methods with steel scrapers and polishing blocks.

Through the use of drum sanders instead of rubbing beds and buffers a
noteworthy advance in surface finishing has been accomplished by a
Maine slate company. Paper-backed silica sandpaper is wound spirally
on drums, three drums are arranged in series, and slate slabs are passed
beneath them on a traveling rubber-covered bed. First, coarse grit is
used to bring down the surface to fair uniformity and smoothness, and for
finishing finer grits are used. A drum sander is several times faster than
a rubbing bed and may with further development also replace planers.

Carborundum machines are used widely to cut cove base and floor tile,
to cut bevels or grooves, to trim blackboards, and to recut slabs to smaller
sizes. The bed carrying the slate slab is stationary, and the rotating
wheel travels back and forth. The machine cuts rapidly and accurately
and leaves a very smooth surface.

Drilling Holes. — Electrical companies using switchboards commonly
drill them for wiring, but sometimes this is done at slate mills. Extreme
accuracy is demanded, as to both position of holes and workmanship.
One mill in Maine uses a spindle drill which can bore 16 holes at once.
The spindles that hold the drills are flexible and so may be adjusted to
position. A pattern or template is used through which the drills mark the

SLATE

277

slate block. The template is then removed, and the drills are guided
accurately by the depressions thus formed.

-ICsJ

-♦o

lij

o
<

-I

"pj

— ».l-

"jr-

O liJ

UJ Q
Z UJ
Oq

o o
z ^
CD X
CO

UJ i: z

COr-O

^ tt O

a cdLq: ? 2

CD o UJ

a < >
< 5 UJ

3 UJ

UJ
£0

— z

3 o
cc or

>-
t

3
(-

X
t-

1
R OR CARBO'
HINE FOR 01

U-

<
o

UJ o

z <

Storage. — Blackboards, electrical slate, panels, steps, and other
structural forms usually are stored at the finishing end of the mill.
Racks are provided where all slabs may be placed on edge, for thus each
one is available when needed.

278

THE STONE INDUSTRIES

Flow Sheet of Slate Mills. — The machines in a mill should be so
arranged that the slate passes most directly from one to another, for much
time and labor are saved thereby. The normal order of operations in
slate manufacture is shown in the flow sheet, figure 55. A plan of a typi-
cal mill arranged for convenient operation is shown in figure 56. Slate
blocks are brought from the quarry into the mill on track a, track h being
used for removal of waste. Blocks are handled by derricks c, between the
tracks. Saws, d, are arranged down one side of the mill and planers, e,
down the other side. After the preliminary stages of sawing and planing,

I slabs are finished in the three wings,
I as shown at the left. Each wing

;:: I E [E ©

J-L
-l-U

^-^

s;=; ;=;0

HE©

0;:; ;=;s

has a rubbing bed /, near its en-
trance followed by a series of finish-
ing machines, such as Carborundum
bevelers, recutters, and polishing
machines, as shown at g and h.
Each wing may be devoted to a
particular product; for example, one
may be used for blackboards, one
for electrical slate, and a third for
structural slate. A railway siding
at the ends of the wings provides a
ready means of shipping mill prod-
ucts. An important feature of the
mill is the facility with which it
56.— Plan of a well-designed slate permits expansion. If increased

b, mill-car tracks; c, derricks; capacity is demanded it may be

!; /, rubbing beds; 0, «, . , ,.

Fig.
mill, a,

d, saws; c, planers; j, x^.^.^-..^. "— -, »'•-', i i j j i-

Carborundum machines, polishing machines; extended and one Or more addl-

i, space for storage and crating. tional wings added, as indicated by

the dotted lines in the figure, without interfering in any way with the
logical order of machine arrangement.

Marbleizing Slate. — For ornamental switchboards, mantels, and
certain other interior decorative products architectural taste sometimes
demands a finish other than the natural slate surface. Repeated painting
and baking to simulate verde antique, bloodstone, or well-known mar-
bles, is known as "marbleizing." The following is a typical process.
The slabs first are painted black, then baked several hours in a cham-
ber heated to 175°F. They are then dipped in a trough of water
having red, white, and green paint floating on the surface. A skilled
operator can stir the water in such a manner as to obtain various
patterns with the floating paint. When a slab of slate is brought into
contact with the surface the paint adheres and reproduces a pattern. It
is baked a second time, varnished, baked a third time, polished with
pumice, and finally baked a fourth time. This gives a "bloodstone"

SLATE 279

finish. If no green paint is used a " Venetian " finish results. Checker-
boards, flags, and various other designs also are made by this process.

"Struco" Slate. — A later development in surface decoration of slate,
to which the trade name ''Struco" has been applied, involves processes
that are quicker and less expensive then marbleizing. Color patterns are
applied as lacquers with a nitrocellulose base and a volatile hydrocarbon
as the vehicle or solvent. Unlike a paint, the drying and hardening are
brought about by evaporation rather than oxidation. A slate slab first is
polished with a belt sander or buffer. The lacquer is then applied to the
surface with a spray nozzle operated with compressed air. The highly
volatile solvent evaporates in 15 or 20 minutes, leaving a firm, hard
surface. A pattern is then applied over the base coat by a printing proc-
ess. A copper plate is engraved as a photographic reproduction of an
attractive veined marble. Lacquer is applied to the plate, and when a
soft-rubber roller is passed over it and then over the slate surface the
pattern is transferred in every detail. A transparent surface coat is then
applied; and, after hardening, it is carefully polished. Struco slate is
unaffected by sudden changes of temperature or by hot or cold water and
is highly resistant to chemicals. Moderately decorative surface finishes
are in demand for shower stalls and wainscoting, while the more orna-
mental types are used for table tops, radiator covers, lamp bases, smoking
sets, clocks, and various novelties. Struco products are not designed to
replace slate in its legitimate field but rather to find use in places where
colors other than the natural shades are desired.

SLATE FLOORS, WALKS, AND WALLS

Ornamental flagging is becoming increasingly important. Slate with
a honed finish and very close joints makes a beautiful floor. Material
from different regions permits floor designs in color patterns that vie in
beauty with the most ornate rugs and have the added value of indestructi-
bility by fire, water, or continuous wear. For paving yards, porches,
courts, roofs, or ornamental walkways, rough-textured, natural cleft
slates are employed. Two main styles are in general use. The "regular "
style consists of rectangular flags of various sizes and colors fitted together
with close joints; the "irregular" is made of random shapes and sizes that
are necessarily less closely fitted and require well-cemented joints.

Slates of various colors are being used as wall stone in such structures
as churches and college buildings, particularly in conjunction with other
kinds of stone, to produce variegated effects in color and texture.

CRUSHED AND PULVERIZED PRODUCTS

Slate crushed to sizes comparable with grains of fine gravel is known
commercially as "granules," the manufacture of which has developed
into an important industry. Granules range in size from 10- to 30-mesh

280

THE STONE INDUSTRIES

and are used to coat various forms of tar roofing. Although most granules
consist of slate, other materials, such as trap rock, shale, and serpentine,
are also used. The industry is, with few exceptions, distinct from the
manufacture of roofing slate; it is, in fact, a competitor, for large quanti-
ties of slate-surfaced roofing are now being sold for use not only on sheds,
garages, and other inexpensive structures but also on moderate-price

dwelling houses of a class
commonly roofed with slate.
Although slate quarry waste is
ground and pulverized to a limited
extent most plants making granules
and flour operate quarries exclu-
sively for these purposes, and in
nearly every instance the rock is
unsuitable for roofing or mill stock.
The types of crushing and grinding
equipment used vary widely.
Where a plant is erected primarily
for making granules, the purpose
is to crush with a minimum pro-
duction of fines, which are dis-
carded largely as waste, but where
there is a good market for pulver-
ized material a large proportion of
fines may not be regarded as a
disadvantage. Even where the
same type of product is desired
no two grinding plants are alike.
Variations are due to differences
in raw materials, amount of capital
available, and varying opinions
regarding efficiency of machines.
A flow sheet of a typical mill using
waste from a large Pennsylvania quarry which produces both roofing
and mill stock is shown in figure 57. The mill is electrically driven
with individual motors for each machine and produces both granules and
slate flour.

No. 5 GYRATORY CRUSHER

~ I '

BUCKET ELEVATOR

]
ROTARY DRIER

I
BUCKET ELEVATOR

\
BIN

BALL MILL
ELEVATOR

HUMMER SCREENS

]
GRANULES 8-35 MESH

FINES

BIN

BLOWER
CAR

OVERSIZE

BIN

TUBE MILL

SCREW CONVEYOR

BATES BAGGER

BARRELING MACHINE

Fig. 57. — Flow sheet of a mill for manufactur-
ing slate granules and slate flour.

WASTE IN QUARRYING AND MANUFACTURING SLATE

An outstanding feature of the slate industry is the high proportion
of waste. It is reported that in one large quarry in Vermont about
15 tons of waste rock are removed for each ton of roofing slate recovered.
In most regions waste averages 70 to 90 per cent of gross production; in

SLATE 281

other places, particularly in underground mining, it may be as low as
50 or 60 per cent. In Wales 1 ton of slate is said to be produced for every
8 tons of waste rock quarried.

Waste is due to a variety of causes. Slate occurs in beds commonly
termed "veins" by quarrymen, though they are not veins in the sense in
which the term is used geologically. Beds of inferior rock alternate with
the good beds, and because of their intimate association the former must
often be removed to secure the latter. Furthermore, only part of the
good beds may be used, for much must be discarded because of such
imperfections as siliceous knots, ribbons, and cracks. A considerable
percentage also is lost in the process of removal ; blasting may shatter it,
or irregular fractures caused by wedging may result in loss. A further
heavy percentage of waste results from the manufacture of roofing
slates, and great quantities of refuse must be removed from beneath the
saws and planers of a structural slate mill.

Slate quarrymen have approached the problem of waste from two
angles. The first involves modifications in methods and machines
whereby a substantial reduction in the percentage of waste may be
attained ; the second concerns various ways in which waste slate may be
utilized.

Prevention of Waste. — Slate is subject to many natural imperfections
over which a quarryman has no control. If only 40 per cent of the mass
of rock blocked out in a quarry is usable, 60 per cent is the lowest mini-
mum to which waste may be reduced, even in theory. In actual practice
the proportion of waste must exceed 60 per cent by varying amounts
depending on the efficiency of quarrying and manufacture. If the final
product constitutes only 15 per cent of gross production and 85 per cent
is waste, obviously 25 of the 40 per cent, or five eighths of the good slate,
is wasted in quarrying and manufacture. A certain percentage of the
good rock must necessarily be lost in these processes, but whatever
share of this five eighths may be saved by improved processes or equip-
ment may be termed "preventable waste."

Much thought and experimenting have been devoted to ways of
reducing the proportion of waste. A first step is to plan development
systematically in conformity with rock structures. The imperfections
of slate and joints, ribbons, or other structural features can not be
changed, and the most orderly quarries are planned to minimize their
effects. A second step in conservation is care in the use of explosives.
Much waste results in some quarry regions from excessive blasting,
because the belief prevails that no other means can be used successfully
for separating primary rock masses. In other regions much more eco-
nomical methods have been worked out. Wire saws now widely used in
Pennsylvania have reduced waste in amounts ranging from 25 to 50 per
cent of the proportion under former processes. Channeling machines are

282 THE STONE INDUSTRIES

a great improvement over blasting methods, and wire saws represent
equal advancement over channeling.

Utilization of Waste. — Owing to imperfections of rock and the inevi-
table loss of material in quarrying and manufacture, a large percentage
of the gross production of slate quarries must be considered waste, even
under the most efficient quarrying and manufacturing methods. The
need for some useful outlet for waste slate has been felt for many years.
Various investigators have given attention to the problem, but results
have had little practical value. Slate consists of silicates that have few
uses compared with some other rocks. For example, limestone may be
used for lime and cement manufacture, agricultural purposes, and furnace
flux; while slate is unsuitable for these purposes. Its commercial
adaptability is, therefore, greatly restricted, and on this account all but
a very small fraction of the waste accumulation since slate was first
quarried is still lying in veritable mountains awaiting possible utilization.

Some years ago interest was centered in a Welsh enterprise for the
conversion of great quantities of waste slate into useful products.
Extravagant claims were made and the plant was operated for a short
time, but the enterprise failed; however, some progress is being made in
waste utilization in Great Britain.

Uses of Waste in Massive and Granular Form. — Waste slate from split-
ting shanties was at one time cut into 3- by 6-inch rectangles, set in
mastic on a backing of prepared roofing, and sold for use on flat roofs
under the name "inlaid slate." One plant operated from 1905 to 1917,
but there has been no production since. Waste slabs have been manu-
factured into perforated-slate lath and veneer. The latter product, which
was used for interior walls, consisted of a thin slab of slate attached to
gypsum board. These projects never advanced beyond the experimental
stage.

Manufacture of granules for slate-surfaced composition roofing has
developed into an important industry, but, as stated previously, only a
small fraction of the raw material is waste from slate quarries or mills.

Waste Slate as a Filler. — Waste rock from mills and quarries is used to
some extent pulverized. Many products, such as paper, rubber, road
asphalt, floor coverings, and paints require as one of their important
constituents a considerable percentage of finely pulverized inert mineral
matter to give "body." to obtain desired consistency, or to supply the
necessary wearing or other qualities demanded. Such materials are
known as "fillers." Slate dust is a satisfactory filler in many such
products.

To encourage wider use of waste slate the United States Bureau of
Mines in 1920 and 1921 cooperated in experiments with about 45 indus-
trial firms. The cooperating companies were manufacturers of rubber
products, linoleum and oilcloth, road asphalt, and plastic roofing.

SLATE 283

Plant and laboratory tests with samples of slate flour were conducted, and
results were submitted to the bureau for compilation. It was found that
finely pulverized slate is a satisfactory filler for mechanical rubber goods
but not for the higher grades of rubber, such as are used in automobile
tires. Slate flour gives good service as a filler in linoleum, oilcloth, and
window shades, except where white is desired. It is well-adapted for
filler in plastic roofing and flooring, and several hundred carloads are so
used every year.

Tests in laboratories of companies preparing road-asphalt mixtures
indicate that for resistance to impact slate flour about equals other
fillers in bonded briquets and is somewhat superior in sheet-surface
mixtures. In cementing value it was found to be superior to both lime-
stone and Portland cement in asphalt-bonded briquets and intermediate
between them in standard sheet surface mixtures. Elutriation tests
indicate that slate flour contains approximately 15 to 25 per cent more
fine dust that constitutes effective filler than limestone, trap rock, or
Portland cement. In low weight for a given volume — a desirable feature
of a filler, — slate is about equivalent to limestone and approximately
10 per cent superior to portland cement. Slate flour is therefore an
exceptionally good filler for road asphalt-surface mixtures.

Ground slate has been used in various ceramic products, but no
conclusive results have been obtained. On account of its low fusion
point it has some possibilities as a glazing material. Considerable
quantities of finely pulverized slate are consumed as paint filler. Pro-
ducers of slate flour in cooperation with consuming industries have
developed many uses in minor products.

It is evident, therefore, that slate flour may be employed in quite
a variety of ways, and some consuming industries are actual or potential
users of large quantities. However, slate flour, like granules, is produced
in very small amount from slate waste ; most of it is derived from quarries
worked exclusively for crushed and pulverized products.

TESTS AND SPECIFICATIONS

The grading of roofing slate varies in different localities. In the
Bangor district of Pennsylvania slates are graded as No. 1, clear; No. 2,
clear; No. 1, ribbon, where the ribbon is not exposed on the finished roof;
and No. 2, ribbon, where it is exposed. They are graded similarly at
Pen Argyl, Pa., with omission of No. 2 ribbon. At Slatington, Pa., and
in Vermont they are graded as No. 1, No. 2, and intermediate. Peach
Bottom slates are graded as No. 1 and No. 2. The Virginia product is
known in the trade as Buckingham slate and graded as No. 1 and No. 2.
Heavy, rough types are known as architectural grades.

To establish more uniform and definite grading the Federal Specifica-
tions Board has framed a specification for roofing slate to be used by

284 THE STONE INDUSTRIES

Government departments. Three grades, designated A, B, and C, are
based mainly on strength, absorption, and depth of softening when
immersed in an acid bath. The specification was pubhshed as of July 26,
1932.

Much valuable information on types of roofs, method of laying,
slope, gutters, flashings, snow guards, and other data a slate roofer
should know are given in an illustrated booklet, "Slate Roofs," issued
in 1926 by the National Slate Association.

Structural slate is graded as ribbon or clear in Pennsylvania and
according to color in Vermont. A series of pamphlets on data and
standards, issued by the Structural Service Bureau of Philadelphia, has
accomplished much in simplifying manufacture, in assisting architects
and builders to place orders for structural slate quickly and easily, and in
making it possible for manufacturers to fill orders promptly from standard
sizes kept in stock.

The requirements for electrical slate are more rigid than for structural
or roofing slate; in addition to easy workability it must have high dielec-
tric strength and must therefore be free of all ribbons or other conducting
materials. No definite specifications have been established, although
much progress has been made in perfecting testing methods.

Slate granules generally are limited in size between 10- and 30-mesh.
Equidimensional rather than flat grains are preferred. Fines are rigidly
excluded ; the percentage allowed usually is so low that granules in storage
ordinarily are air-cleaned while being loaded to remove the fines produced
in handling.

No generally used specifications have been adopted for slate flour as
it is used in many different products which have varied requirements.
Manufacturers of similar products differ widely among themselves in size
requirements for fillers. Producers of slate flour are obliged to modify
their milling equipment to satisfy the demands of individual customers.

MARKETING

Consideration of the uses of slate makes it evident that the chief
consuming industries are the building trades and manufacturers of elec-
trical equipment. As building construction is a nationwide industry, the
chief centers of consumption are fixed largely by freight rates, building
programs, and the activity of selling agents. Roofing slate is used
widely on buildings east of the Mississippi River, but because of former
high freight rates the demand west of the Mississippi was limited.
Recently rail-water rates have been reduced, and increasing quantities of
slate are reaching Pacific coast points by way of the Panama Canal.
Likewise, reduction of rates is opening up extensive markets south of the
Carolinas, where little slate has been used except in New Orleans. Here
the necessity for conserving the rain-water supply has encouraged the use

SLATE 285

of insoluble, sanitary slate roofs. Structural slate is less affected by-
freight and thus has a somewhat wider market than roofing slate.

The centers of electrical slate consumption are the large eastern and
middle western industrial cities, such as New York, Boston, Philadelphia,
Schenectady, Pittsburgh, Chicago, and St. Louis. The market for
blackboards is general throughout the United States and Canada.
Most school slates are exported. A marked growth in use of slate for
floors and walks has been evident since 1925 and is rapidly spreading
over the entire country, because the pieces are classed as "scrap" slate
and are carried at lowest freight rates. There is a scattered demand for
slate blackboards and for structural slate in the insular possessions of the
United States and in Cuba.

The chief marketing points for slate are Pen Argyl, Bangor, Slating-
ton, Easton, Bethlehem, Philadelphia, and Delta, Pa.; New York City;
Monson and Portland, Me.; Boston, Mass.; Granville, N. Y.; Poultney
and Fair Haven, Vt.; and Richmond and Norfolk, Va. There are
practically no seasonal fluctuations in the demand for electrical slate,
but owing to building inactivity the demand for structural, roofing, and
scrap slate is somewhat restricted in winter. Subnormal demand for
blackboards usually is in evidence during March, April, and May.

The slate industry has very difficult marketing problems. Lack of
more consistent growth in the industry is to be attributed chiefly to the
keen competition slate must meet in every line of consumption. Various
types of roofing are advertised much more widely, and many are syn-
thetic products that can be manufactured at low cost. Similarly, slate
meets much competition in structural and electrical applications.

Lack of efficient selling and advertising agencies also retards effective
marketing; those sections of the industry that are most inactive in this
respect are the least prosperous. There is, however, evidence of a move-
ment toward bettering this condition through establishment of joint
marketing agencies in some localities to bring about better contacts
between producers, distributors, and roofing and setting contractors, thus
promoting sales and insuring better service to ultimate consumers. The
outstanding problem in all slate regions is to find a large enough market to
absorb the normal output of the quarries. Marketing companies and
associations are exerting a growing influence, particularly in Pennsylvania
and Virginia. Sales organizations in Vermont and New York have been
effective only in marketing structural slate and that used for floors, walks,
and walls. Those who have the best interest of the industry at heart
contend that excellent service under the most exacting requirements will
enhance the salability of the products. Expansion of markets therefore
depends to quite a degree on proper classification of slate and on the
diversion of each type to the use for which it is best adapted. This
requires an exact and intimate knowledge of properties and qualities,

286 THE STONE INDUSTRIES

and to obtain the necessary fundamental data the National Slate Associa-
tion and Committee D-16 of the American Society for Testing Materials
are sponsoring studies of properties and methods of tests. The United
States Bureau of Standards and several college laboratories, notably those
of Lafayette College, Lehigh University, Pennsylvania State College,
Rensselaer Polytechnic Institute, and Massachusetts Institute of
Technology, are collaborating in these studies.

Persistent price-cutting, even at levels below the cost of production,
has characterized slate marketing. As this is due in a measure to an
insufficient knowledge of quarrying and milling costs an effort has been
made to establish better and more uniform cost keeping, and a cost-
accounting system for the industry has been published. ^^

Structural slate is sold to slate-setting contractors. Roofing slate is
sold to roofers and building-supply dealers through jobbers or brokers or
directly by quarry operators. To lessen breakage and prevent reducing
the requisite 3-inch head lap, nail holes for attachment of the slate
usually are punched before shipment.

Slate flour, granules, and scrap are sold by the ton, though scrap used
for floors and walks sometimes is figured in superficial feet. Granules
are sold in bulk in carload lots direct to manufacturers of composition
roofing. Slate flour is disposed of to paint manufacturers and marketed
in small amounts to miscellaneous users, such as manufacturers of roofing
mastic, rubber, and linoleum. It usually is sold in paper bags or wooden
barrels but may be marketed in bulk to large consumers. Roofing slate
sells by the square (enough to cover 100 square feet when placed on a
sloping roof with standard 3-inch head lap), mill stock and blackboards
by the square foot, baseboard by the running foot, and school slates by
the dozen.

IMPORTS AND EXPORTS

Slate imports range from $50,000 to $130,000 in annual value. There
are fluctuations from year to year, both in total and in relative amounts
from different countries. During recent years the chief sources of
foreign slates have been Italy, France, Portugal, Norway, and the
United Kingdom. About 15 per cent by value in 1929 was roofing slate.
The remainder was made up of blackboards and of slabs and other prod-
ucts not clearly specified.

From 1925 to 1929 annual exports of roofing slate ranged from 5,000
to 10,000 squares a year and had an average value of $9 to $12 a square.
Between 75 and 85 per cent were sold in Canada. Exports of other slate
products over a period of years are shown in the following table compiled
by the United States Bureau of Mines:

^* Bowles, Oliver, A System of Accounts for the Slate Industry. Rept. of Investi-
gations 2971, Bureau of Mines, 1929, 25 pp.

SLATE

287

Slate Other Than Roofing Exported from the United States, 1929-1930 and

1936-1937 BY Uses

Use

1929

1930

1936

1937

Quantity

Value

Quantity

Value

Quantity

Value

Quantity

Value

School slates, cases*

19,570

$108,135

16,280

$ 95,935

2,651

$ 20,204

4,434

$ 35,011

Electrical slate,

square feet

16,720

18,037

18,830

20,406

5,528

4,449

3,986

2,356

Blackboards,

square feet

188,720

74,610

177,760

59,810

53,486

15,502

26,033

6,853

Billiard tables,

square feet

20,150

34,455

15,760

9,802

26,729

10,601

30,443

16,580

Structural, square

feet

18,390

15,882

12,670

5,280

25,592

5,831

26,462

4,393

Slate granules and

"flour," short

14,250

84,185

27,540

162,000

9,412

67,012

11,184

77,576

$335 304

S353 , 233

$123,599

$142,769

* Cases weigh 130 to 165 pounds each; average is 135 pounds.

Practically all exports of roofing slate and granules, over 95 per cent of
the structural, and over 50 per cent of the electrical slate were shipped to
Canada in 1929. School slates also vi^ere shipped to Canada; but India,
Netherland East Indies, Australia, and New Zealand took the largest
quantities in 1929. South America, West Indies, and Asia furnished
markets for electrical slate; and Mexico, Central America, and the
Philippine Islands for billiard-table slate. The above data are typical
of the export trade in any year.

TARIFF

Before 1913 the duty on imported slates, chimney pieces, mantels,
slabs for tables, roofing slates, and all other manufactures of slate w^as
20 per cent ad valorem. The act of October 1913 reduced it to 10 per cent ;
that of September 1922 raised it to 15 per cent; and the act of 1930
raised it to 25 per cent ad valorem.

PRICES

Roofing-slate prices are quoted at times in trade magazines, though
many sales are made by individual bargaining at prices that may diverge
widely from those quoted in the market columns. The price per square
varies with the size, and the larger sizes command higher prices. The
average selling price of all kinds in 1929 was $10.65 a square. In 1932 it
was $7.43 a square.

Mill products are not quoted regularly, but list prices are supplied to
customers. The average selling price a square foot for the various

288 THE STONE INDUSTRIES

products in 1929 was as follows: Electrical, 80 cents; structural, 40 cents;
vaults, 26 cents; blackboards, 30 cents; billiard-table tops, 40 cents; and
flagging, 10 cents. Granules and slate flour sold at about $5.80 a ton.
The above figures are based on selling prices at the quarry or mill.
Prices were somewhat lower in 1930, 1931 and 1932.

Bibliography

AuBURY, Lewis E. The Structural and Industrial Materials of California. Cali-
fornia State Min. Bur. Bull. 38, 1906, pp. 149-154.

Behre, C. H., Jr. Observations on Structures in the Slates of Northampton County,
Pa. Jour. Geol., vol. 34, no. 6, pp. 481-506.

Mineral Industry 1927, 1928, 1929, 1930, and 1931 (chapters on slate).

McGraw-Hill Book Company, Inc., New York.

■ Geologic Factors in the Development of the Eastern Pennsylvania Slate

Belt. Am. Inst. Min. and Met. Eng. Tech. Paper 66, 1928, 18 pp.

Slate Deposits of Northampton County. Pennsylvania Topog. and Geol.

Survey Bull M 9, 1927, 312 pp.

- — Slate in Pennsylvania. Pennsylvania Topog. and Geol. Survey Bull. M 16,

1933, 400 pp.
Bowles, Oliver. The Characteristics of Slate. Proc. Am. Soc. Test. Mat., vol. 23,
pt. 2, 1923, pp. 524-534.

Fundamental Factors in the Testing of Mineral Products with Special

Reference to Slate and Related Materials. Proc. Am. Soc. Test. Mat., vol. 29, pt.
2, 1929, pp. 902-908.

The Technology of Slate. Bur. of Mines Bull. 218, 1922, 132 pp.

The Wire Saw in Slate Quarrying: Bur. of Mines Tech. Paper 469, 1930,

31 pp.

Consumption Trends in the Roofing Slate Industry. Bur. of Mines Rept.

of Investigations 3221, 1933, 3 pp. (mimeographed).

A System of Accounts for the Slate Industry. Bur. Mines Rept. of Investi-
gations 2971, 1929, 25 pp. (mimeographed).

The Marketing of Metals and Minerals (chapter on slate). McGraw-Hill

Book Company, Inc., New York, 1925, pp. 524-529.

Coons, A. T. Mineral Resources of the United States (chapters on slate). Pub-
lished annually by the U. S. Bur. of Mines (prior to 1924 by the U. S. Geol.
Survey, Minerals Yearbook since 1931.)

Dale, T. Nelson. The Slate Belt of Eastern New York and Western Vermont.
U. S. Geol. Survey, Nineteenth Ann. Rept., pt. 3, 1897-1898, 1898, pp. 153-307.

Dale, T. Nelson, and others. Slate in the United States. U. S. Geol. Survey Bull.
586, 1914, 220 pp.

Eckel, E. C. Building Stones and Clays. John Wiley & Sons, Inc., New York,
1912, pp. 95-126.

HiRSCHWALD, J. Handbuch der bautechnischen Gesteinspriifung. Verlag von
Gebriider Borntraeger, Berlin, 1912, 923 pp.

Kessler, D. W. and Sligh, W. H. Physical Properties and Weathering Char-
acteristics of Slate. U. S. Bur. of Standards Res. Paper 477, 1932, 35 pp.

Matthews, Edwar,d B. An Account of the Character and Distribution of Maryland
Building Stones (section on slate). Maryland Geol. Survey, vol. 2, 1898, pp.
214-232.

National Slate Association. Slate Roofs. Philadelphia, 1926, 84 pp.

North, F. J. The Slates of Wales. 2d ed., Univ. of Wales, Cardiff, 1927, 84 pp.

SLATE 289

Purdue, A. H. The Slates of Arkansas. Contributions to Economic Geologj^
1909, pt. 1 (f), U. S. Geol. Survey Bull. 430, 1910, pp. 317-334.

Richardson, C. H. Building Stones and Clays. Syracuse Univ. Book Store,
Syracuse, N. Y., 1917, pp. 267-302.

Shearer, H. K. The Slate Deposits of Georgia. Geol. Survev Georgia Bull. 34,
1918, 192 pp.

CHAPTER XI

SOAPSTONE

Production of soapstone is commonly considered part of the talc
industry, as talc is a constituent, but the uses of these commodities are
for the most part quite diverse, because at least 95 per cent of all talc
produced is sold pulverized while a large proportion of all soapstone
quarried is sold as blocks of various shapes and sizes. Soapstone is used
widely in construction and for building accessories, therefore it may
properly be called part of the dimension-stone industry.

COMPOSITION AND PROPERTIES

The term "soapstone" in its original sense apparently was synony-
mous with steatite or massive talc; however, it more properly includes all
dark gray to greenish talcose massive rocks which have a soapy feel and
which with few exceptions, are soft enough to be carved easily with a
knife. Nearly all soapstone produced for commerce is metamorphic rock
containing 10 to 80 per cent talc, a hydrous magnesium silicate of
composition expressed by the formula H2Mg3(Si03)4. The most char-
acteristic physical properties of talc are its softness (it may be scratched
easily with the finger nail) and its soapy feel. Although talc is the most
characteristic, and frequently the chief, constituent of soapstone other
minerals are present in varying amounts; chlorite, amphibole, pyroxene,
and mica are the more common constituents, with smaller amounts of
pyrite, quartz, calcite, and dolomite. Soapstone must therefore be
regarded as a rock rather than a mineral; and because of its variable
composition, its hardness and strength are also variable.

HISTORY

Soapstone was carved into ornaments by the ancient Egyptians and
Assyrians, and for many centuries the Chinese have used it for the same
purpose. It has long been used in limited quantities as a building mate-
rial. The cathedral of Trondhjem, Norway, is built of soapstone from
Gudbransdal.

Soapstone was first used in the United States by the American
Indians, who, recognizing its heat-retaining qualities, shaped it into
bowls, pots, cooking stones, and other objects now on display in many
museums. The term "potstone," which is still applied to soapstone in
some localities, originated from these early uses. Deposits in Albemarle

290

SOAPSTONE

291

County, Va., were opened on a semicommercial scale about 1880.
During later years the industry migrated into Nelson County, and recent
activity has been confined to the vicinity of Schuyler. A small produc-
tion has been noted at various times in Maryland, North Carolina, Rhode
Island, Vermont, and California, but Virginia has always dominated the
industry. A quarry near Marriottsville, Md., was reopened in 1933.

During recent years so much of the production has been in the hands
of a single company that figures can not be published without revealing
individual statistics. However, the following table, compiled from
United States Geological Survey publications, is presented as a record of
output for a number of years.

Domestic Soapstone Sold in the United States, 1916-1924

Year

Quantity,
short tons

Value

1916

19,127

S 489,606

1917

19,885

402,506

1918

12,330

501,059

1919

16,504

530,163

1920

19,707

709,400

1921

17,423*

627,826*

1922

22,700

712,144

1923

22,857

932,098

1924

25,630

1,288,885

* Sawed and manufactured talc included under soapstone.

USES

The uses of soapstone are related intimately to its physical properties.
Its easy workability, light color, and resistance to weathering or water
action fit it admirably for many structural purposes; laundry tubs, sinks,
aquariums, wainscoting, mantels, baseboards, stair treads, tiles, and
spandrels are made of soapstone. Floor tile and steps sometimes are
calcined to make them harder than rock in its natural state. Because
of its resistance to chemical action and low absorptive properties soap-
stone is adaptable for laboratory table tops and sinks, hoods, ovens, acid
tanks, vats, trays, development tanks for photographs and blue prints,
drains, and furnace blocks for lining retorts in paper mills. Some
soapstones have high dielectric strength, which, combined with easy
workability, makes them desirable for electrical insulation units, such as
switchboards, panels, barriers, fuse guards, bases, circuit-breaker com-
partments, insulating floor slabs, battery-room flooring or shelving, and
similar products. Because of its ability to resist and to retain heat,
soapstone is employed for griddles, foot warmers, fireless cooker stones,

292 THE STONE INDUSTRIES

fireplaces, hearths, and furnace linings; some of these uses, however, are
declining.

Soapstone is divided into three grades — soft, regular, and hard.
The high heat resistance of the soft grade makes it especially desirable for
furnace linings and other uses where high temperatures prevail. The
hard grade, containing a large proportion of the harder siliceous minerals,
such as hornblende and actinolite, is best suited for stair treads, floor tile,
and other products subject to wear. The regular grade, midway in
properties between the hard and soft, is by far the most abundant.
Virtually all fabricated equipment having interlocking joints, such as
laundry tubs, sinks, and sanitary partitions, is made of soapstone of this
quality.

Granular soapstone, hardened by heat treatment, is used for surfacing
prepared roofing. Pulverized waste material is employed as an admix-
ture in concrete and as a filler and sold to some extent for dusting coal
mines.

ORIGIN AND OCCURRENCE

Most soapstone is regarded as an alteration product of basic igneous
rocks rich in magnesium. The extensive deposits near Schuyler, Va.,
consist of irregular or lenslike dikes bordered with mica schist and
peridotite. These deposits have been studied and described in some
detail, but very little is known of the occurrences in other States. The
important deposits in Virginia form a belt which extends through Nelson,
Albemarle, and Orange Counties and for many years have constituted
the chief source of supply. Small deposits have been noted in Fairfax,
Franklin, Amelia, and Henry Counties. Soapstone is quarried near
Thetford Mines, Quebec, Canada, for production of furnace blocks and
pulverized products.

QUARRY METHODS

The normal size of quarries at Schuyler, Va., is 100 feet long by 100 to
120 feet wide, the width being governed by the size of the dike. Enough
soapstone to provide a good face is left in place along the hanging wall.
If several quarries are opened on one dike, walls 22 feet wide are left
standing between operations. The depth to which a quarry may be
worked depends on safety of the walls; the average depth is nearly
200 feet.

Overburden is removed chiefly by steam shovels and drag scrapers,
though hydraulic methods have been used. Occasionally good stone is
found near the surface, but usually the upper floors are removed as waste.
No explosives are used in either waste or good rock. Overburden and
waste usually are dumped into pits that have been worked out and
abandoned.

SOAPSTONE

293

A stripped quarry floor is channeled across the strike with steam
or electric-air machines. The distance between channel cuts is 4 to
6 feet, and the average depth 6>^ feet. After a center row of key blocks
is removed all other channeled masses are undercut to their full depth.
An undercutter is a reciprocating machine that works like a channeler.
In soft rock a Jeffrey longwall undercutter with stellite teeth is used
satisfactorily. One end of the undercut mass is channeled across and
the end block broken out. The mass is then subdivided by drilling holes
parallel to the natural parting planes of the rock, and by splitting with
wedges. As the natural grain dips at angles of 30 to 60° blocks
are roughly diamond-shaped. An average block is 4 by 4 by 6 feet.
Each is graded according to hardness, color, and soundness. Swinging-
boom derricks lift them from the quarry floor and place them on cars or
stock piles, depending upon current mill requirements.

MILLING PROCESSES

As with other types of dimension stone, sawing is the first step in
manufacturing soapstone products. Gang saws, like those used for

Fig. 58.

-Two soapstone saw mills with overhead traveling crane between them, Schuyler,
Va. (Photo by H. Herbert Hughes.)

marble and limestone, are employed, and 30- to 46-mesh sea sand is
used as abrasive. Saws travel back and forth at about 84 complete
strokes a minute in the day time, while at night when other machinery is
shut down the speed is increased to about 100 strokes a minute. Gangs
cut through the stone at about 4 inches an hour. Most of the stock is cut
into thin slabs, which results in less waste from oblique-angled blocks
than if cubic stock were manufactured. For most uses saw cuts are made

294 THE STONE INDUSTRIES

to parallel the grain. Sawed slabs are transferred to either a stock mill
or a custom mill. Figure 58 illustrates two soapstone saw mills with an
overhead traveling crane between.

A stock mill produces standard products, such as laundry tubs, sinks,
and furnace blocks. Trimming is done with a steel-toothed hand saw
similar to that used in wood working. The slab surfaces are finished
on rubbing beds and tongued and grooved with Carborundum wheels.
In assembling tubs one small bolt secures each corner but is not exposed
in the interior. All joints are set in cement, consisting of linseed oil,
litharge, and whiting, which expands as it seasons, insuring watertight
joints. An important function of a stock mill is the manufacture of
furnace blocks. These are made in numerous sizes and shapes 3 inches
to 3 feet long. Blocks are cut with circular diamond saws, and care is
taken that the direction of grain is always at right angles to the exposed
surface when a block is set in place; otherwise, it is liable to spall.

All other soapstone, consisting chiefly of structural material, is
fabricated in the custom mill according to specifications. The general
procedure is similar to that in a stock mill, except that blue prints are
followed on all jobs. Furthermore, much stone used in the custom mill
is harder than that employed for laundry tubs or furnace blocks. There-
fore, circular silicon carbide saws are used instead of hand saws for
trimming, and Carborundum grinders supplement rubbing beds. Rub-
bed slabs pass to a checker, who designates from blue prints the additional
fabricating to be done. Completed slabs are assembled in the mill or
on the job, depending on the nature of the order.

Some higher-grade waste soapstone is pulverized as filler, chiefly for
use in the rubber industry. For this purpose crushers, hammer mills,
tube mills, screens, and air classifiers are the chief types of equipment
used.

MARKETING

Markets for soapstone are world-wide, but only a small proportion
of the production is exported. The largest consumption is east of the
Mississippi River, particularly in the Atlantic Seaboard States. The
increasing use of soapstone for architectural purposes during recent years
has resulted in fluctuations in demand that parallel the seasonal activity
of building. Shipments are now made almost entirely by rail and
wherever practical in carload lots. Most soapstone products, except
furnace blocks, are crated.

There is at present practically no competition within the industry in
marketing soapstone. However, it meets with very keen competition
from other materials, including marble, slate, sandstone, limestone, and
certain synthetic products, in virtually every market except for furnace
blocks.

SOAPSTONE 295

The unit of measurement for manufactured soapstone is a square foot
13^^ inches thick. All products, regardless of size, shape, or use, are
reduced to this unit. Furnace blocks comprise the largest low-priced
output, while complicated development tanks and similar equipment
requiring much skilled labor bring the highest prices. Nearly all sales
are made direct to builders and contractors; there are no brokers or
middlemen.

ROCKS RELATED TO SOAPSTONE

A metamorphic rock known as "greenstone," consisting essentially of
actinolite and chlorite, outcrops prominently at Lynchburg, Va. It has
an attractive unfading green color that renders it suitable for structural
and ornamental building. Many years ago it was used as a local build-
ing stone. Basements, chimneys, and entire houses made of it show no
evidence of change or deterioration. During recent years the quarries
have been reopened, and a mill has been constructed for the manu-
facture of structural and decorative slabs and other products.

Bibliography

Bowles, Oliver. Chapters on Talc and Soapstone. Mineral Industry, 1930 and

1931, McGraw-Hill Book Company, Inc., New York.
Bowles, Oliver, and Stoddard, B. H. Chapters on Talc and Soapstone. Bur.

of Mines Mineral Resources of the United States, for 1928, 1929, 1930, and 1931.

(Included in chapter on dimension stone in Minerals Yearbook after 1931.)
BuRFOOT, J. D. The Origin of the Talc and Soapstone Deposits of Virginia. Jour.

Econ. GeoL, vol. 25, 1930, pp. 806-826.
Hughes, H. Herbert. Soapstone. Bur. of Mines Inf. Circ. 6563, 1931, 18 pp.
Ryan, C. W. Soapstone Mining in Virginia. Am. Inst. Min. and Met. Eng. Tech.

Pub. 160, 1929, 31 pp.

CHAPTER XII

BOULDERS AS BUILDING MATERIALS
ORIGIN AND NATURE OF BOULDERS

The term "boulders" is applied to loose fragments of rock as con-
trasted with solid beds or masses, which are designated "rock in place,"
and is restricted to masses that have become loosened from the parent
ledge by natural processes, such as by water, frost action, or glaciation.
Boulders usually are plentiful in rugged regions where bedrock is close
to the surface and along old shore lines and river beds. They are rare or
absent in ancient lake beds that are now land areas or in deltas or out-
wash plains of rivers, for only the finer, lighter products of rock disintegra-
tion are disposed in such places.

A great difference is to be observed between boulders in northern
states compared with those in the south. In its southward movement
the great ice sheet of the glacial age reached northern New Jersey, central
Pennsylvania, and, roughly, a line that followed the Ohio and Missouri
Rivers. North of this line most of the surface soil is glacial till, and much
of it remains in the condition in which it was left by the ice, though large
areas have been re worked and assorted by water action. Materials
carried by the ice may have been picked up at widely separated points and
carried long distances. Boulders in glacial regions may therefore consist
of a great variety of rocks; granites, gneisses, syenites, limestones, sand-
stones, and conglomerates may all be found within a restricted area.
Usually they are rounded and show other evidences of excessive
wear.

In the area south of the southern limit of glaciation some boulders
may have been transported limited distances by rivers or other agencies,
but for the most part they are of local origin. In limestone regions
boulders consist of fragments of underlying limestone; likewise, in granite
regions, few, if any, are to be found that are not related directly to
outcrops in the immediate neighborhood. Ordinarily they are more
angular than those of glaciated regions.

As nature had thus fashioned building blocks and left them conven-
iently placed on the surface of the ground they probably constituted
materials for the most primitive habitations built by ancient races.
Their ready availability led to early use by pioneers, and they are still
important construction materials.

296

BOULDERS AS BUILDING MATERIALS 297

STONE FENCES

A use of stone of which Httle mention has been made is as fencing.
The subject has been neglected because it falls midway between two great
jBelds of activity — mining and agriculture. A very small part of such
stone is quarried rock; nearly all of it consists of boulders picked up by
farmers while working in their fields. Employment of stone in this way
serves a twofold purpose — clearing land of annoying obstructions and
fencing it. Such work must be classed as farm labor; it is not properly
part of the mining industry. Compilers of agricultural statistics are
interested in the size of fields and mileage of fences but have subdivided
fences by kinds to a very limited extent. Hence, for quite logical reasons,
no record has been kept of the mileage of stone fences or the amount of
material used in their construction.

Most stone fences now in existence were built many years ago. It
was necessary for pioneer farmers to clear the land, and labor being
cheap, the cost of building stone walls along the borders of fields was not
excessive.

Stone has long been a choice material for ornamental walls and fences
in town and suburban estates. Since such walls are erected for archi-
tectural effect rather than practical value waste rock is used little, but a
surprisingly large amount of quarried rock cut into regular dimensions
and having a rather high marketable value is so consumed. Walls and
fences of this material look so solid and rugged that they are invaluable
artistic additions to any home.

Certain objections have been raised to stone fences. Unless well-
built, sheep can scale them; they harbor weeds, brush, insects, and
burrowing animals; and their removal for the enlargement of fields is
expensive. On the other hand, such fences, properly built with foun-
dations that will not heave with frost action, are the most enduring of
all types ; moreover, they are attractive and are fireproof, often preventing
a blaze spreading from field to field.

The extent to which stone is used for fencing is quite variable in
different parts of the country. Throughout the Great Plains region of
the Middle West very little stone occurs, and the Rocky Mountain and
Far West States have few stone fences. In the New England and other
Eastern States, however, granite and limestone boulders abound and
have been widely used for this purpose. Throughout Connecticut,
Rhode Island, and other Northeastern States there are miles and miles
of fences made of the abundant granites and other igneous rocks. In
northern Virginia many roads and fields are neatly fenced for long
stretches with limestone boulders.

Data for determining the mileage of stone fences in the United States
are meager. In so far as the writer has ascertained statistics cover only

298 THE STONE INDUSTRIES

the North Central States and certain selected parts of New York. The
first of these areas comprises States where very little stone is found on
farms, and consequently few such fences are built. According to a
report^^ of the United States Department of Agriculture only about
0.17 per cent of the fences were of stone in the following 11 States: South
Dakota, Nebraska, Kansas, Minnesota, Iowa, Missouri, Wisconsin,
Illinois, Michigan, Indiana, and Ohio. In this group Wisconsin stands
highest, with 0.8 per cent. A second recorded study by Myers^" covered
53 farms in New York averaging 173.4 acres each. The average length
of stone fence per farm was 122.5 rods, or 8.1 per cent of the total fencing.
In certain sections the percentage ran as high as 36.

If it is assumed that the figure 8.1 per cent, obtained by Cornell
University for parts of New York, typifies the more rugged and older
settled parts of the East, which occupy about one sixth of the area of
the United States, and that the figure, 0.17 per cent, obtained by the
United States Department of Agriculture for the North Central States,
is a fair average for the rest of the country, a basis has been established
for estimating the total extent of stone fences. Figures thus obtained
may be far from correct, but they at least supply an estimate on which to
hinge comments until better figures are obtainable.

According to census figures, some years ago there were 5,371,000,000
rods of fence in the United States. On the basis given above the approxi-
mate length of stone fences would be 78,620,000 rods or about 246,000
miles.

To determine the cubic contents of this volume of fencing a certain
amount of guesswork again is required, for fences are not of uniform
size; some built long ago are massive, while others, especially those built
more recently are of much smaller proportions. Many limestone fences
in Virginia are about 2 feet wide at the bottom, 1 foot wide at the top,
and 43^^ to 5 feet high. If average dimensions are assumed to be 2}'^
feet wide at the bottom, 13-^ feet at top, and 5 feet high, the total volume
would reach the staggering figure of nearly 13,000,000,000 cubic feet.
Practically all the fences are dry walls built without mortar. The stones
are laid carefully and packed so closely that the air spaces between them
probably do not occupy more than one fourth of the entire volume.
Assuming that three fourths of the volume is solid stone weighing about
160 pounds to the cubic foot the weight of stone used in fences approaches
780,000,000 tons, which is equivalent to about 280 times the pro-
duction of dimension stone in the United States in 1931. The figures

33 Humphrey, H. N., Cost of Fencing Farms in the North Central States. U. S.
Dept. of Agriculture Bull. 321, 1909.

'"' Myers, W. I., An Economic Study of Farm Layout. Cornell Univ. Agric. Exp.
Sta. Memoir 34, 1920.

BOULDERS AS BUILDING MATERIALS 299

given above may, of course, be very much in error, but at least they show
a use of stone of very great magnitude.

This lowly application that finds no place in statistics and little
mention in song or story fills in toto an important place in rural life.
But what of the future? As stone fences gradually deteriorate through
action of the elements, the high cost of labor for repairs or rebuilding
leads to replacement of many of them with wire fences. The widening of
highways and enlargement of fields may also demand their removal. The

!• iG. 59. — Graceful limestone fences in Virginia. (Photo by the author.)

material from some of them has been used for building purposes, or
crushed for hard-road construction. Diminishing use is in prospect,
but any movement toward wholesale destruction is to be regretted, for
nothing is more enduring than the rocks from which this old world is
made. Not only are stone fences substantial and long lived, but they are
picturesque and lend an attractiveness to rural landscapes that would be
sadly missed.

It is evident that the dignity, stability, and ruggedness of stone
fences are fully appreciated in some localities. During active repaving
and road widening in northern Virginia in 1930 and 1931, numerous
stone fences were moved back and rebuilt in attractive forms that
enhance the beauty of an already charming landscape. Pillored gate-
ways and graceful curves, as illustrated in figure 59, feature both new
and old fences. Such structures add the charm of artistry to the utility
of substantial and enduring stone.

USE OF BOULDERS IN BUILDINGS

As stated previously, boulders were used by the early settlers long
before the days of quarrying. Although modern methods have made it

300

THE STONE INDUSTRIES

possible to shape bed rock into building units quickly and at moderate
cost, the use of boulders has by no means been abandoned; they are still
popular and are widely used. Perhaps their most prominent use is in
rustic fireplaces and exterior chimneys, the latter constituting prominent
features of many beautifully designed residences. They are also used
extensively for basements, lower courses, and porch walls. Entire
exterior house walls of boulders are by no means uncommon; in fact, the
present demand for ruggedness and variety in architecture has led to
increasing use. An unusual use is shown in figure 60.

Fig. 60. — A unique type of boulder construction combining chimney with stairway.

hy H. Herbert Hughes.)

{Photo

As mentioned heretofore, the greatest variation in materials is in
glaciated country. In such regions boulder houses may have in the same
wall granites, gneisses, syenites, trap rocks, limestones, sandstones, and
mica schists interspersed occasionally with beautiful red jasper
conglomerates.

The use of boulders is not confined to modest dwelling houses.
Many mansions costing thousands of dollars, mountain resorts, hotels,
and public buildings are built largely of them. Farmers may be paid
by the wagon load for hauling rocks from their farms to build such
structures. Although the work of construction is slow and expensive
many buildings of this type are of beautiful rustic design; they will
endure for many years, and their maintenance cost is low.

CHAPTER XIII

FOREIGN BUILDING AND ORNAMENTAL STONES^i
SCOPE OF DISCUSSION

Many foreign countries are rich in structural and ornamental materials
of mineral origin. In the Old World structural stones were used far
back in prehistoric ages, and the acid test of time has proved that many-
are remarkably enduring. Multitudes of beautiful, serviceable American
stones are no doubt just as capable of resisting the storms of centuries,
but our New World civilization is as yet far too young to prove their
qualities. In European countries magnificent cathedrals and other
public buildings erected centuries ago are centers of interest for travelers
from all nations. It is fitting, therefore, that some attention be given
to the sources of supply of materials which people of foreign lands have
found to be essential for the noblest and most substantial types of
architecture.

The primary purpose of this book is to cover adequately the stone
industries of the United States, for space would not permit a treatise
covering in detail these industries throughout the world. Nevertheless,
many foreign stones are now, or have been, used extensively in America,
and it is therefore desirable to give some attention to those that are
used in conjunction with, or as substitutes for, stone of domestic origin.
As brevity is necessary, attention will be given chiefly to stones from other
lands that find prominent use in the United States.

IMPORTS OF STONE

To indicate the extent to which foreign stones are used in this country,
a table of imports compiled by the United States Bureau of Mines is
shown on page 302. It comprises a table covering stone, to which has
been added the value of imported slate.

The future consumption of foreign stone in America is hard to predict.
Demands during the depression years were subnormal and, coupled with
depressed markets, imports have been and will continue to be influ-
enced by the tariff revision of 1930 and subsequent revisions.

*i Acknowledgment is hereby made of helpful information obtained from certain
unpublished manuscripts on foreign building stones compiled some years ago by
T. C. Hopkins for the U. S. Geol. Survey.

301

302

THE STONE INDUSTRIES

Stone Imported for Consumption in the United States, 1929-1930
AND 1936-1937, BY Kinds

1929

1930

1936

1937

Kind

Quan-
tity

Value

Quan-
tity

Value

Quan-
tity

Value

Quan-
tity

Value

Marble, breccia,

and onyx:
In blocks, rough,

etc., cubic feet
Sawed, cubic feet
Slabs or paving

tiles, superficial

feet

667,900
10,859

649 , 899

$1,591,070
24,799

253 , 267
566,010

1,908

717,436
797

591,616

$1,578,856
2,983

254 , 179
329 , 279

12,157

60,784
172

150,364
5,609

$256,922
712

58,979
43,879

140

75,302
165

214,588
9,362

$297 , 501
488

67 , 789

All other manu-

69 , 403

Mosaic cubes of
marble or onyx.

180

Total

$2,437,054

$2,177,454

$360,632

$435,361

Granite:

Dressed, cubic
feet

$ 292,644
378,943

138,831

$ 266,318
202,037

16,233
43 , 089

$ 67,293
63 , 627

36,853
43,871

$178,607

Rough, cubic feet

216,022

67,212

Total

$ 671,587

$ 428,355

59,322

$130,920

80,724

$245 819

Quartzite, short

*
*

102,032t
74,163t

$ 174,334t
64, 997 t

50,704
48,917

$ 91,120
67,185

139,533
13,404

$249 003

Travertine, cubic
feet

18 677

Stone (other) :

$ 62,674

184,620
233,324

214,424

$ 23,396

203,417
73,908

2,229
3,939

$ 5,471

3,688
7,050

2,647
6,287

$ 6,310

Rough (monu-
mental or
building), cubic
feet

240,399

6 617

Rough (other).

19 639

Total

$ 480,618

$ 300,721

$ 16,209

$ 32 566

Slate

$ 95,073

$ 48,065

$ 4,851

$ 4 824

Grand total

$3,684,332

$3,193,926

$670,917

$986 250

* Not separately classified.

t Figures cover June 18 to December 31: not separately classified prior to change in tariff.

FOREIGN LIMESTONES

Canada. — The Tyndall limestone of Ordovician age, occurring about
30 miles northwest of Winnipeg, Manitoba, generally is regarded as the
best building limestone in western Canada. The main productive ridge
is about }4 mile wide and 1 mile long, although less easily available rock
occurs over a much wider area. Two main types of stone are obtained —

FOREIGN BUILDING AND ORNAMENTAL STONES 303

an upper buff-mottled stone in beds 12 to 13 feet thick in all, and a lower
blue-mottled stone 5 to 6 feet thick. Both kinds extended below the
floor of the quarry at the stage of progress covered by Park's original
description (see bibliography), and the total thickness of the formation
was about 130 feet. The rock has a characteristic mottled appearance
due to evenly distributed dark patches. Blocks are sawed, cut, and
carved in large, well-equipped finishing mills, either at the quarries or in
Winnipeg. Some waste material is burned into lime. The product is
used widely for public buildings in Winnipeg and other midwestern cities.

Limestones are plentiful in Ontario, and numerous quarries have
been opened in many localities. Most of them, however, are small and
supply stone only for local use. Dark, heavily bedded limestones of the
Black River formation have been used so widely in Kingston that it has
been called the Limestone City. Other noteworthy occurrences are the
Trenton, which is used to some extent in Ottawa; the Niagara limestone
at Hamilton; and the Onondaga near St. Marys. The largest building
limestone quarry in Ontario is at Queenston near Niagara Falls. While
it has been worked for many years, activities have been enlarged greatly
under new ownership since 1925. Rock of high quality occurs in iflat-
lying beds about 15 feet thick all told, with a moderate overburden.
The stone is a pleasing silver gray that mellows with time. It has low
absorptive properties and is highly resistant to weathering. The quarry
product is sold as rough blocks or slabs for fabrication in independent
mills. It is used in constructing many large buildings in Hamilton,
Toronto, and other Canadian cities.

Numerous buildings in Montreal are made of limestone quarried in or
near the city. The stone belongs to the Chazy and Trenton formations
and is of three main types. The first, a grayish, medium-grained, semi-
crystalline limestone is of the highest grade and is suitable for cut stone.
The second, a hard, dark, fine-grained variety, and the third, an inter-
banding of the first and second, are used mainly for rock-faced work.
Trenton limestones have been quarried extensively in Portneuf County,
Quebec, and used for building purposes in Quebec city and in Montreal.

Cuba. — Buff and blue oolitic limestone is quarried in the suburbs of
Havana. It is somewhat like Indiana limestone but is finer-grained and
softer. It may be cut readily with an ax or hand saw but hardens upon
exposure. As the deposit is conveniently situated and easily worked the
stone is used quite extensively for building houses in Havana.

Bermuda. — Bermuda limestone is a porous aggregation of shell and
coral fragments, ranging from a chalky, white, fine-grained, soft type to a
darker, coarser, and harder form. It is worked so easily that blocks are
cut out with long-handled chisels and subdivided to desired sizes and
shapes with hand saws. Many houses are built of the softer types; even
the roofs consist of thin slabs. When whitewashed this variety is

304

THE STONE INDUSTRIES

durable enough for a mild, moderate climate like that of Bermuda. The
harder rock has been used for fortifications and other Government works
on the islands.

France. — The Caen stone, a Jurassic oolitic variety quarried near
Caen, Falaise, and Bayeux in Normandy, is one of the best known lime-
stones of France. It is a soft, fine-grained, light-colored rock admirably
adapted for carved work. While not suitable for outdoor use in a climate
like that of the United States it has been popular for many centuries as
an interior decorative stone, particularly in Gothic architecture. It was

Fig. 61. — Underground limestone mines, Commercy, France. (Courtesy of J. B. Newsom.)

shipped to England in large quantities shortly after the Norman con-
quest and employed in such notable structures as the Cathedral of
Canterbury and Westminster Abbey. The workable beds have a
maximum thickness of 20 to 25 feet and cover a wide area. Most of the
workings are underground, though some stone is taken from open
quarries. It is shipped by water to various European ports and to
America.

Jurassic oolitic limestones are quarried also in the Department of
Meuse on the east side of the Paris Basin. Highly fossiliferous stone,
consisting chiefly of crinoid fragments, is obtained from open-pit quarries
at Euville and Lerouville and from underground workings at Commercy.
The latter are shown in figure 61. This has been used for fortifications,
canals, and many notable buildings in Paris. "Comblanchien" is a well-
known Jurassic type. As shown in figure 62, canals are of great assist-
ance in transportation.

Large quarries of similar stone have long been worked near Auxerre
in the Department of Yonne southeast of Paris. It is reported that 43

FOREIGN BUILDING AND ORNAMENTAL STONES 305

quarries were operated in 1889. Large sawmills were employed to shape
blocks for the construction of canals and as building stone used in France,
England, Belgium, and the United States.

Jurassic oolites and Lower Cretaceous lime

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Books

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "The stone industries : dimension stone, crushed stone, geology, technology, distribution, utilization"

See other formats